gen1recomp/docs/gold-walkthrough/asm-walk/section-30-lapras.md

Section 30 - Lapras

Source: ../section-30-lapras.txt Maps covered: MAP_UNION_CAVE_1F, MAP_UNION_CAVE_B1F, MAP_UNION_CAVE_B2F (approach only: MAP_ROUTE_32, whose warp into the cave is cited but which belongs to section 03) Badges / key milestones in this section: no badge. The milestone is the static level-20 Lapras on Union Cave B2F, which only exists on a Friday and only once per in-game day (ENGINE_UNION_CAVE_LAPRAS). Five optional trainers (Andrew, Calvin, Nick, Gwen, Emma) and two item balls sit on the way in.

This is a revisit section: Union Cave 1F/B1F were first walked in section 03. Everything here is reachable only with Surf, i.e. after the Fog Badge.

1. Route order

#	Map constant	asm file	Enter via	Leaves via	Why (walkthrough beat)
1	MAP_ROUTE_32	maps/Route32.asm	walked south from Violet City (connection south, Route32, ROUTE_32, 0 in data/maps/attributes.asm)	warp_event 6, 79, UNION_CAVE_1F, 4	"head to Violet City and then go south through Route 32 into Union Cave"
2	MAP_UNION_CAVE_1F	maps/UnionCave1F.asm	warp 4 at 17, 3 (from Route 32)	warp_event 3, 33, UNION_CAVE_B1F, 4	walk past Daniel / Russell / Bill, surf the south-west lake, take the bottom-left ladder
3	MAP_UNION_CAVE_B1F	maps/UnionCaveB1F.asm	warp 4 at 3, 33	warp_event 17, 31, UNION_CAVE_B2F, 1	Pokemaniac Andrew stands at 5, 32 right next to the arrival ladder; surf east to Calvin at 17, 30, then the ladder beside him
4	MAP_UNION_CAVE_B2F	maps/UnionCaveB2F.asm	warp 1 at 5, 3	same warp back up, or Escape Rope / Dig	Hyper Potion, Nick, Gwen, Emma, then the Lapras object at 11, 31

The walkthrough ends inside Union Cave B2F ("You can then use Escape Rope to leave Union Cave"); it does not spill into a neighbouring section's map.

2. Maps

MAP_UNION_CAVE_1F

• Script: maps/UnionCave1F.asm
• Blocks: maps/UnionCave1F.blk
• Header: data/maps/maps.asm:107 -> map UnionCave1F, TILESET_CAVE, CAVE, LANDMARK_UNION_CAVE, MUSIC_UNION_CAVE, TRUE, PALETTE_NITE, FISHGROUP_LAKE (the TRUE field is the phone-service flag: no phone calls in Union Cave)
• Dimensions: constants/map_constants.asm:94 -> map_const UNION_CAVE_1F, 10, 18 (10x18 blocks = 20x36 walk cells)
• Attributes: data/maps/attributes.asm:426 -> map_attributes UnionCave1F, UNION_CAVE_1F, $09
• Connections: none (no connection rows follow the attributes line)
• Map group: MapGroup_Dungeons (data/maps/maps.asm:77)

Warps (def_warp_events)

idx	x	y	destination map	dest warp
1	5	19	UNION_CAVE_B1F	3
2	3	33	UNION_CAVE_B1F	4
3	17	31	ROUTE_33	1
4	17	3	ROUTE_32	4

Coord events (def_coord_events)

None - the block is empty.

BG events (def_bg_events)

None. (UnionCave1FUnusedSign / UnionCave1FUnusedSignText exist in the file but are marked ; unreferenced and are not in any bg_event row.)

Object events (def_object_events)

const	sprite	x	y	movement	type	script label	event flag
UNIONCAVE1F_POKEFAN_M1	SPRITE_POKEFAN_M	4	4	SPRITEMOVEDATA_SPINRANDOM_FAST	OBJECTTYPE_TRAINER, sight 1	TrainerHikerDaniel	-1
UNIONCAVE1F_SUPER_NERD	SPRITE_SUPER_NERD	4	21	SPRITEMOVEDATA_STANDING_DOWN	OBJECTTYPE_TRAINER, sight 2	TrainerPokemaniacLarry	-1
UNIONCAVE1F_POKEFAN_M2	SPRITE_POKEFAN_M	15	8	SPRITEMOVEDATA_STANDING_LEFT	OBJECTTYPE_TRAINER, sight 3	TrainerHikerRussell	-1
UNIONCAVE1F_FISHER1	SPRITE_FISHER	16	31	SPRITEMOVEDATA_STANDING_UP	OBJECTTYPE_TRAINER, sight 4	TrainerFirebreatherRay	-1
UNIONCAVE1F_FISHER2	SPRITE_FISHER	15	15	SPRITEMOVEDATA_SPINRANDOM_FAST	OBJECTTYPE_TRAINER, sight 2	TrainerFirebreatherBill	-1
UNIONCAVE1F_POKE_BALL1	SPRITE_POKE_BALL	17	21	SPRITEMOVEDATA_STILL	OBJECTTYPE_ITEMBALL	UnionCave1FGreatBall	EVENT_UNION_CAVE_1F_GREAT_BALL
UNIONCAVE1F_POKE_BALL2	SPRITE_POKE_BALL	4	2	SPRITEMOVEDATA_STILL	OBJECTTYPE_ITEMBALL	UnionCave1FPotion	EVENT_UNION_CAVE_1F_POTION
UNIONCAVE1F_POKE_BALL3	SPRITE_POKE_BALL	4	17	SPRITEMOVEDATA_STILL	OBJECTTYPE_ITEMBALL	UnionCave1FXAttack	EVENT_UNION_CAVE_1F_X_ATTACK
UNIONCAVE1F_POKE_BALL4	SPRITE_POKE_BALL	12	33	SPRITEMOVEDATA_STILL	OBJECTTYPE_ITEMBALL	UnionCave1FAwakening	EVENT_UNION_CAVE_1F_AWAKENING

Scripts of interest

• UnionCave1F_MapScripts - def_scene_scripts and def_callbacks are both empty. Nothing on 1F is time- or flag-gated; the floor is pure walking.
• PokemaniacLarryAfterBattleText and FirebreatherBillAfterBattleText are the in-game hints the walkthrough is acting on: "Every Friday, you can hear #MON roars from deep inside the cave." and "On weekends, you can hear strange roars from deep in the cave." Only Larry's Friday line matches the code (see B2F callback below).

Flags and events

constant	defined in	read/written by	meaning for a bot
EVENT_UNION_CAVE_1F_GREAT_BALL	constants/event_flags.asm	itemball object row	set once the ball is taken; masks the object
EVENT_UNION_CAVE_1F_POTION	constants/event_flags.asm	itemball object row	same
EVENT_UNION_CAVE_1F_X_ATTACK	constants/event_flags.asm	itemball object row	same
EVENT_UNION_CAVE_1F_AWAKENING	constants/event_flags.asm	itemball object row	same
EVENT_BEAT_HIKER_DANIEL, EVENT_BEAT_HIKER_RUSSELL, EVENT_BEAT_POKEMANIAC_LARRY, EVENT_BEAT_FIREBREATHER_BILL, EVENT_BEAT_FIREBREATHER_RAY	constants/event_flags.asm	3rd argument of each trainer macro row	set = already beaten, no eyesight trigger

Items

item	how obtained	source (label / bg_event / hidden)	one-time flag
GREAT_BALL	item ball at 17,21	UnionCave1FGreatBall (itemball GREAT_BALL)	EVENT_UNION_CAVE_1F_GREAT_BALL
POTION	item ball at 4,2	UnionCave1FPotion	EVENT_UNION_CAVE_1F_POTION
X_ATTACK	item ball at 4,17	UnionCave1FXAttack	EVENT_UNION_CAVE_1F_X_ATTACK
AWAKENING	item ball at 12,33	UnionCave1FAwakening	EVENT_UNION_CAVE_1F_AWAKENING

Trainers (all optional on this pass; the walkthrough only mentions walking past them)

const	class	id	party (data/trainers/parties.asm label)	script label	rematch/phone
HIKER, DANIEL	HIKER	DANIEL	"DANIEL@"	TrainerHikerDaniel	phone service disabled on this map (TRUE in the header)
HIKER, RUSSELL	HIKER	RUSSELL	"RUSSELL@"	TrainerHikerRussell	as above
POKEMANIAC, LARRY	POKEMANIAC	LARRY	"LARRY@"	TrainerPokemaniacLarry	as above
FIREBREATHER, BILL	FIREBREATHER	BILL	"BILL@"	TrainerFirebreatherBill	as above
FIREBREATHER, RAY	FIREBREATHER	RAY	"RAY@"	TrainerFirebreatherRay	as above

(Party rows for these five were not transcribed - they belong to section 03 and the walkthrough tells the bot to walk past them, not fight them.)

Wild encounters

Grass/cave, data/wild/johto_grass.asm:444 def_grass_wildmons UNION_CAVE_1F, rate 6 percent for morn/day/nite alike. Gold list (identical across all three time slots):

slot	level	species
1	6	GEODUDE
2	6	SANDSHREW (Silver: RATTATA)
3	5	ZUBAT
4	4	RATTATA
5	7	ZUBAT
6	6	ONIX
7	6	ONIX

Water, data/wild/johto_water.asm:12 def_water_wildmons UNION_CAVE_1F, rate 2 percent: 15 WOOPER, 20 QUAGSIRE, 15 QUAGSIRE.

Fishing group is FISHGROUP_LAKE (header row).

MAP_UNION_CAVE_B1F

• Script: maps/UnionCaveB1F.asm
• Blocks: maps/UnionCaveB1F.blk
• Header: data/maps/maps.asm:108 -> map UnionCaveB1F, TILESET_CAVE, CAVE, LANDMARK_UNION_CAVE, MUSIC_UNION_CAVE, TRUE, PALETTE_NITE, FISHGROUP_LAKE
• Dimensions: constants/map_constants.asm:95 -> map_const UNION_CAVE_B1F, 10, 18
• Attributes: data/maps/attributes.asm:427 -> map_attributes UnionCaveB1F, UNION_CAVE_B1F, $09
• Connections: none
• Symbols: 44:5415 UnionCaveB1F_MapScripts, 44:56df UnionCaveB1F_MapEvents (pokegold.sym)

Warps (def_warp_events)

idx	x	y	destination map	dest warp
1	3	3	RUINS_OF_ALPH_OUTSIDE	7
2	3	11	RUINS_OF_ALPH_OUTSIDE	8
3	7	19	UNION_CAVE_1F	1
4	3	33	UNION_CAVE_1F	2
5	17	31	UNION_CAVE_B2F	1

Coord events (def_coord_events)

None.

BG events (def_bg_events)

None.

Object events (def_object_events)

const	sprite	x	y	movement	type	script label	event flag
UNIONCAVEB1F_POKEFAN_M1	SPRITE_POKEFAN_M	10	4	SPRITEMOVEDATA_SPINRANDOM_FAST	OBJECTTYPE_TRAINER, sight 1	TrainerHikerPhillip	-1
UNIONCAVEB1F_POKEFAN_M2	SPRITE_POKEFAN_M	17	10	SPRITEMOVEDATA_STANDING_DOWN	OBJECTTYPE_TRAINER, sight 3	TrainerHikerLeonard	-1
UNIONCAVEB1F_SUPER_NERD1	SPRITE_SUPER_NERD	5	32	SPRITEMOVEDATA_STANDING_LEFT	OBJECTTYPE_TRAINER, sight 3	TrainerPokemaniacAndrew	-1
UNIONCAVEB1F_SUPER_NERD2	SPRITE_SUPER_NERD	17	30	SPRITEMOVEDATA_STANDING_LEFT	OBJECTTYPE_TRAINER, sight 3	TrainerPokemaniacCalvin	-1
UNIONCAVEB1F_POKE_BALL1	SPRITE_POKE_BALL	2	16	SPRITEMOVEDATA_STILL	OBJECTTYPE_ITEMBALL	UnionCaveB1FTMSwift	EVENT_UNION_CAVE_B1F_TM_SWIFT
UNIONCAVEB1F_BOULDER	SPRITE_BOULDER	7	10	SPRITEMOVEDATA_STRENGTH_BOULDER	OBJECTTYPE_SCRIPT	UnionCaveB1FBoulder	-1
UNIONCAVEB1F_POKE_BALL2	SPRITE_POKE_BALL	17	23	SPRITEMOVEDATA_STILL	OBJECTTYPE_ITEMBALL	UnionCaveB1FXDefend	EVENT_UNION_CAVE_B1F_X_DEFEND

Scripts of interest

• UnionCaveB1F_MapScripts - both def_scene_scripts and def_callbacks are empty. Nothing on B1F is gated.
• TrainerPokemaniacAndrew (44:5417) - trainer POKEMANIAC, ANDREW, EVENT_BEAT_POKEMANIAC_ANDREW, PokemaniacAndrewSeenText, PokemaniacAndrewBeatenText, 0, .Script. .Script is the boilerplate after-battle path: endifjustbattled / opentext / writetext PokemaniacAndrewAfterBattleText / waitbutton / closetext / end. No flags beyond the beaten flag, no items, no warps.
• TrainerPokemaniacCalvin (44:542b) - identical shape with EVENT_BEAT_POKEMANIAC_CALVIN and PokemaniacCalvinAfterBattleText ("You demonstrated on me!" is PokemaniacCalvinBeatenText, matching the walkthrough quote).
• UnionCaveB1FBoulder - jumpstd StrengthBoulderScript. Not on the walkthrough's path to Lapras (it sits at 7, 10, up near the Ruins of Alph ladders), but it is the one Strength-gated object on the floor.

Flags and events

constant	defined in	read/written by	meaning for a bot
EVENT_BEAT_POKEMANIAC_ANDREW	constants/event_flags.asm:751	TrainerPokemaniacAndrew	set after the win; suppresses the eyesight trigger
EVENT_BEAT_POKEMANIAC_CALVIN	constants/event_flags.asm:752	TrainerPokemaniacCalvin	same
EVENT_BEAT_HIKER_PHILLIP, EVENT_BEAT_HIKER_LEONARD	constants/event_flags.asm	the two Hiker trainer rows	not on the Lapras path
EVENT_UNION_CAVE_B1F_TM_SWIFT	constants/event_flags.asm	itemball object row	one-time TM_SWIFT
EVENT_UNION_CAVE_B1F_X_DEFEND	constants/event_flags.asm	itemball object row	one-time X_DEFEND

Items

item	how obtained	source (label / bg_event / hidden)	one-time flag
TM_SWIFT	item ball at 2,16	UnionCaveB1FTMSwift	EVENT_UNION_CAVE_B1F_TM_SWIFT
X_DEFEND	item ball at 17,23	UnionCaveB1FXDefend	EVENT_UNION_CAVE_B1F_X_DEFEND

Neither is mentioned by the walkthrough; both are on the way to the B2F ladder.

Trainers

const	class	id	party (data/trainers/parties.asm label)	script label	rematch/phone
POKEMANIAC, ANDREW	POKEMANIAC ($1e, constants/trainer_constants.asm:245)	ANDREW (id 2)	"ANDREW@", TRAINERTYPE_NORMAL at data/trainers/parties.asm:1086: L24 MAROWAK, L24 MAROWAK	TrainerPokemaniacAndrew	no phone (map header phone flag TRUE)
POKEMANIAC, CALVIN	POKEMANIAC	CALVIN (id 3)	"CALVIN@", TRAINERTYPE_NORMAL at data/trainers/parties.asm:1092: L26 KANGASKHAN	TrainerPokemaniacCalvin	no phone
HIKER, PHILLIP	HIKER	PHILLIP	"PHILLIP@"	TrainerHikerPhillip	off-path
HIKER, LEONARD	HIKER	LEONARD	"LEONARD@"	TrainerHikerLeonard	off-path

TRAINERTYPE_NORMAL means level+species only: no custom moves, no held items.

Prize money: POKEMANIAC base reward is db 15 (data/trainers/attributes.asm:179 ; Pokemaniac). ComputeTrainerReward (engine/battle/read_trainer_party.asm:300) computes base * wCurPartyLevel where the level is the last party row, and WinTrainerBattle (engine/battle/core.asm:2292) pays that out four times (ld c, 4 at the .okay loop). So Andrew = 15244 = 1440, Calvin = 15264 = 1560 - both match the walkthrough exactly.

Wild encounters

Grass/cave, data/wild/johto_grass.asm:499 def_grass_wildmons UNION_CAVE_B1F, rate 6 percent morn/day/nite. Gold list (same in all three slots):

slot	level	species
1	8	GEODUDE
2	8	SANDSHREW (Silver: RATTATA)
3	7	ZUBAT
4	8	ONIX
5	9	ZUBAT
6	6	RATTATA
7	6	RATTATA

Water, data/wild/johto_water.asm:19, rate 2 percent: 15 WOOPER, 20 QUAGSIRE, 15 QUAGSIRE.

MAP_UNION_CAVE_B2F

This is the section's real content.

• Script: maps/UnionCaveB2F.asm
• Blocks: maps/UnionCaveB2F.blk (2b:466d UnionCaveB2F_Blocks)
• Header: data/maps/maps.asm:109 -> map UnionCaveB2F, TILESET_CAVE, CAVE, LANDMARK_UNION_CAVE, MUSIC_UNION_CAVE, TRUE, PALETTE_NITE, FISHGROUP_SHORE (note: FISHGROUP_SHORE here, not FISHGROUP_LAKE like the two floors above)
• Dimensions: constants/map_constants.asm:96 -> map_const UNION_CAVE_B2F, 10, 18 (20x36 walk cells)
• Attributes: data/maps/attributes.asm:428 -> map_attributes UnionCaveB2F, UNION_CAVE_B2F, $09
• Connections: none
• Symbols: 44:5759 UnionCaveB2F_MapScripts, 44:575e UnionCaveB2FLaprasCallback, 44:5770 UnionCaveLapras, 44:59cb UnionCaveB2F_MapEvents, 25:595d UnionCaveB2F_MapAttributes

Warps (def_warp_events)

idx	x	y	destination map	dest warp
1	5	3	UNION_CAVE_B1F	5

One warp. There is no second exit: leaving is either back up this ladder, or Escape Rope / Dig (the walkthrough's suggestion).

Coord events (def_coord_events)

None - the block is empty. Nothing on B2F is a trip-wire; every event is an object you walk into the sight line of or press A on.

BG events (def_bg_events)

None.

Object events (def_object_events)

const	sprite	x	y	movement	type	script label	event flag
UNIONCAVEB2F_ROCKER	SPRITE_ROCKER	17	23	SPRITEMOVEDATA_STANDING_LEFT	OBJECTTYPE_TRAINER, sight 5, PAL_NPC_RED	TrainerCooltrainermNick	-1
UNIONCAVEB2F_COOLTRAINER_F1	SPRITE_COOLTRAINER_F	5	13	SPRITEMOVEDATA_SPINRANDOM_FAST	OBJECTTYPE_TRAINER, sight 1, PAL_NPC_RED	TrainerCooltrainerfGwen	-1
UNIONCAVEB2F_COOLTRAINER_F2	SPRITE_COOLTRAINER_F	3	28	SPRITEMOVEDATA_STANDING_DOWN	OBJECTTYPE_TRAINER, sight 2, PAL_NPC_RED	TrainerCooltrainerfEmma	-1
UNIONCAVEB2F_POKE_BALL1	SPRITE_POKE_BALL	16	2	SPRITEMOVEDATA_STILL	OBJECTTYPE_ITEMBALL	UnionCaveB2FElixer	EVENT_UNION_CAVE_B2F_ELIXER
UNIONCAVEB2F_POKE_BALL2	SPRITE_POKE_BALL	12	19	SPRITEMOVEDATA_STILL	OBJECTTYPE_ITEMBALL	UnionCaveB2FHyperPotion	EVENT_UNION_CAVE_B2F_HYPER_POTION
UNIONCAVEB2F_LAPRAS	SPRITE_SURF	11	31	SPRITEMOVEDATA_SWIM_WANDER, radius x=1 y=1, PAL_NPC_BLUE	OBJECTTYPE_SCRIPT	UnionCaveLapras	EVENT_UNION_CAVE_B2F_LAPRAS

Notes a bot needs:

• Lapras uses SPRITE_SURF (constants/sprite_constants.asm:87, id 53) - the same overworld sprite the player rides. It is not a Lapras sprite.
• SPRITEMOVEDATA_SWIM_WANDER with radius 1,1 means the object drifts within one cell of 11, 31. A driver must not hard-code an exact tile to face; it should walk to the neighbourhood and press A at whichever adjacent water cell the sprite is occupying.
• Its event flag is EVENT_UNION_CAVE_B2F_LAPRAS. CheckObjectFlag (engine/overworld/map_objects_2.asm:31) masks an object when the flag is set, so "Lapras present" = flag clear.

Scripts of interest

UnionCaveB2F_MapScripts (44:5759)

	def_scene_scripts          ; empty
	def_callbacks
	callback MAPCALLBACK_OBJECTS, UnionCaveB2FLaprasCallback

UnionCaveB2FLaprasCallback (44:575e) - the whole Friday rule, six opcodes:

	checkflag ENGINE_UNION_CAVE_LAPRAS
	iftrue .NoAppear
	readvar VAR_WEEKDAY
	ifequal FRIDAY, .Appear
.NoAppear:
	disappear UNIONCAVEB2F_LAPRAS
	endcallback
.Appear:
	appear UNIONCAVEB2F_LAPRAS
	endcallback

Control flow, spelled out:

1. checkflag ENGINE_UNION_CAVE_LAPRAS - a daily engine flag (constants/engine_flags.asm:107, in the wDailyFlags2 block; bit DAILYFLAGS2_UNION_CAVE_LAPRAS_F = 1, constants/ram_constants.asm:315). Set means "already caught/fought it today" -> .NoAppear.
2. readvar VAR_WEEKDAY (constants/script_constants.asm:59, id $0b) then ifequal FRIDAY (constants/ram_constants.asm:218, FRIDAY = 5, Sunday-based). Only Friday reaches .Appear.
3. appear clears the object's event flag (Script_appear, engine/overworld/scripting.asm:879, ld b, 0 ; clear); disappear sets it (Script_disappear, :887, ld b, 1 ; set).

Because the callback is MAPCALLBACK_OBJECTS, it re-runs on every map load of B2F (engine/overworld/map_setup.asm:81 farcall LoadObjectMasks follows it). So a bot that walks out and back in on a non-Friday will find Lapras gone.

UnionCaveLapras (44:5770) - the encounter itself:

	faceplayer
	cry LAPRAS
	loadwildmon LAPRAS, 20
	startbattle
	disappear UNIONCAVEB2F_LAPRAS
	setflag ENGINE_UNION_CAVE_LAPRAS
	reloadmapafterbattle
	end

Load-bearing details:

• loadwildmon LAPRAS, 20 - a level 20 wild Lapras, matching the walkthrough. There is no writevar VAR_BATTLETYPE here, so unlike Ho-Oh / Lugia / the Red Gyarados this is an ordinary wild battle: no forced item, no forced shiny, no BATTLETYPE_CANLOSE mercy.
• disappear and setflag run unconditionally after the battle, with no iffalse / checkflag guard on the outcome. So Lapras is consumed for the day whether you caught it, KO'd it, ran, or blacked out mid-battle. That is exactly why the walkthrough says to save first - a soft reset is the only recovery.
• setflag ENGINE_UNION_CAVE_LAPRAS is the daily flag, not a permanent event. CheckDailyResetTimer (engine/overworld/time.asm:88) zeroes wDailyFlags1 and wDailyFlags2 whole once a day has elapsed, so it comes back next Friday.

TrainerCooltrainermNick (44:577f), TrainerCooltrainerfGwen (44:5793), TrainerCooltrainerfEmma (44:57a7) - all three are the plain trainer <class>, <id>, EVENT_BEAT_*, <seen>, <beaten>, 0, .Script shape with an endifjustbattled / opentext / writetext ...AfterBattleText / waitbutton / closetext / end follow-up. No items, no warps, no flags beyond their own EVENT_BEAT_*.

CooltrainerfEmmaAfterBattleText is the in-map hint for the whole section: "Just once a week, a #MON comes to the water's edge. / I wanted to see that #MON..."

UnionCaveB2FElixer = itemball ELIXER; UnionCaveB2FHyperPotion = itemball HYPER_POTION (macros/scripts/maps.asm:155, two raw bytes db item, quantity, not bytecode).

Flags and events

constant	defined in	read/written by	meaning for a bot
ENGINE_UNION_CAVE_LAPRAS	constants/engine_flags.asm:107 (backed by data/events/engine_flags.asm:117 -> wDailyFlags2 bit DAILYFLAGS2_UNION_CAVE_LAPRAS_F)	read by UnionCaveB2FLaprasCallback, set by UnionCaveLapras	"Lapras already used up today". Cleared wholesale by CheckDailyResetTimer (engine/overworld/time.asm:88-97)
EVENT_UNION_CAVE_B2F_LAPRAS	constants/event_flags.asm:1282	written by the callback's appear/disappear	object visibility mask. Clear = visible (engine/overworld/map_objects_2.asm:31 CheckObjectFlag)
VAR_WEEKDAY	constants/script_constants.asm:59 ($0b)	readvar in the callback	wCurDay, 0 = SUNDAY .. 6 = SATURDAY; FRIDAY = 5 (constants/ram_constants.asm:218)
EVENT_BEAT_COOLTRAINERM_NICK	constants/event_flags.asm:857	TrainerCooltrainermNick	beaten flag
EVENT_BEAT_COOLTRAINERF_GWEN	constants/event_flags.asm:877	TrainerCooltrainerfGwen	beaten flag
EVENT_BEAT_COOLTRAINERF_EMMA	constants/event_flags.asm:891	TrainerCooltrainerfEmma	beaten flag
EVENT_UNION_CAVE_B2F_ELIXER	constants/event_flags.asm:1025	itemball object row	one-time
EVENT_UNION_CAVE_B2F_HYPER_POTION	constants/event_flags.asm:1026	itemball object row	one-time

There are no SCENE_* values on this map: def_scene_scripts is empty, so wMapScene is never consulted here.

Items

item	how obtained	source (label / bg_event / hidden)	one-time flag
ELIXER	item ball at 16,2	UnionCaveB2FElixer (itemball ELIXER)	EVENT_UNION_CAVE_B2F_ELIXER
HYPER_POTION	item ball at 12,19	UnionCaveB2FHyperPotion (itemball HYPER_POTION)	EVENT_UNION_CAVE_B2F_HYPER_POTION

The walkthrough names only the Hyper Potion ("Land on the right side to grab a Hyper Potion"). The Elixer at 16, 2 sits near the arrival ladder at 5, 3 and is never mentioned - free pickup for a bot on the way in.

Trainers

const	class	id	party (data/trainers/parties.asm label)	script label	rematch/phone
COOLTRAINERM, NICK	COOLTRAINERM ($1b, constants/trainer_constants.asm:184)	NICK (id 1)	"NICK@", TRAINERTYPE_MOVES at data/trainers/parties.asm:742	TrainerCooltrainermNick	no phone (map phone flag TRUE)
COOLTRAINERF, GWEN	COOLTRAINERF ($1c, :205)	GWEN (id 1)	"GWEN@", TRAINERTYPE_NORMAL at :867	TrainerCooltrainerfGwen	no phone
COOLTRAINERF, EMMA	COOLTRAINERF	EMMA (id 15)	"EMMA@", TRAINERTYPE_NORMAL at :954	TrainerCooltrainerfEmma	no phone

Parties verbatim:

NICK (TRAINERTYPE_MOVES - custom movesets, no items):

#	level	species	moves
1	26	CHARMANDER	EMBER, SMOKESCREEN, RAGE, SCARY_FACE
2	26	SQUIRTLE	WITHDRAW, WATER_GUN, BITE, CURSE
3	26	BULBASAUR	LEECH_SEED, POISONPOWDER, SLEEP_POWDER, RAZOR_LEAF

GWEN (TRAINERTYPE_NORMAL):

#	level	species
1	26	EEVEE
2	22	FLAREON
3	22	VAPOREON
4	22	JOLTEON

EMMA (TRAINERTYPE_NORMAL): L28 POLIWHIRL, single mon.

Prize money (base * last-party-level * 4, see the B1F note): COOLTRAINERM and COOLTRAINERF both have db 12 ; base reward (data/trainers/attributes.asm:161 ; Cooltrainerm, :167 ; Cooltrainerf). Nick = 12264 = 1248, Gwen = 12224 = 1056 (last row is the L22 Jolteon), Emma = 12284 = 1344. All three match the walkthrough.

AI: both Cooltrainer classes carry the full AI_BASIC | AI_SETUP | AI_SMART | AI_AGGRESSIVE | AI_CAUTIOUS | AI_STATUS | AI_RISKY set and SWITCH_SOMETIMES; Pokemaniac is the weaker AI_BASIC | AI_SETUP | AI_OFFENSIVE | AI_AGGRESSIVE | AI_STATUS. None of the five hold items (db NO_ITEM, NO_ITEM).

Wild encounters

Grass/cave, data/wild/johto_grass.asm:554 def_grass_wildmons UNION_CAVE_B2F, rate 4 percent. This table is not split by version, and all three time-of-day slots are identical:

slot	level	species
1	22	ZUBAT
2	22	RATICATE
3	22	GOLBAT
4	21	GEODUDE
5	20	RATTATA
6	23	ONIX
7	23	ONIX

Water (the surf legs the walkthrough spends most of its time on), data/wild/johto_water.asm:26 def_water_wildmons UNION_CAVE_B2F, rate 4 percent (double the 1F/B1F water rate):

slot	level	species
1	15	TENTACOOL
2	20	QUAGSIRE
3	20	TENTACRUEL

Fishing group is FISHGROUP_SHORE (data/maps/maps.asm:109). No headbutt or rock-smash tables apply - it is a cave with no trees.

The walkthrough's Max Repel advice: REPEL_STEPS in the port mirrors RepelEffect / SuperRepelEffect / MaxRepelEffect; MAX_REPEL is 250 steps. With the B2F encounters capped at level 23 and the lead mon typically above that, Repel suppresses essentially all of the grass rolls.

3. Blockers and gates

Gate	Enforced by (file:label)	Requirement	Unlock condition
Cannot cross any of the water on 1F / B1F / B2F	engine/events/overworld.asm:322 SurfFunction.TrySurf (ld de, ENGINE_FOGBADGE / call CheckBadge / jr c, .nofogbadge), and the walk-into-water path TrySurfOW at :469	Fog Badge plus a party mon that knows SURF	beat Morty in Ecruteak Gym (section 07)
Lapras object is absent 6 days out of 7	maps/UnionCaveB2F.asm:15 UnionCaveB2FLaprasCallback -> readvar VAR_WEEKDAY / ifequal FRIDAY	in-game weekday must equal FRIDAY (constants/ram_constants.asm:218, value 5)	set the GB clock / wait for Friday. Re-checked on every B2F map load (MAPCALLBACK_OBJECTS)
Lapras is absent again after one encounter	same callback, first two opcodes: checkflag ENGINE_UNION_CAVE_LAPRAS / iftrue .NoAppear; the flag is set by UnionCaveLapras	flag must be clear	CheckDailyResetTimer (engine/overworld/time.asm:88) zeroes wDailyFlags1+wDailyFlags2 once a real day has passed
Lapras is consumed even on a failed attempt	UnionCaveLapras: startbattle is followed unconditionally by disappear + setflag - no iffalse on wBattleResult	none - this is the failure mode, not a gate	save before pressing A; soft-reset on a bad outcome
Only one way out of B2F	maps/UnionCaveB2F.asm def_warp_events has exactly one row (5, 3 -> UNION_CAVE_B1F, 5)	-	Escape Rope / Dig short-circuits the return walk (B2F's tileset is TILESET_CAVE)
Boulder at B1F 7, 10	UnionCaveB1FBoulder -> jumpstd StrengthBoulderScript	Strength / Plain Badge	not on the Lapras path; noted for completeness

Nothing in this section checks a badge count, a key item, or an EVENT_* story flag. The only two real gates are Surf and Friday.

4. Bot checklist

Preconditions for the whole section: Fog Badge, a party mon with SURF, the in-game weekday equal to FRIDAY, ENGINE_UNION_CAVE_LAPRAS clear, several Ultra Balls, a status move (Sleep/Paralysis) and a save written immediately before the Lapras press.

#	Map	Target	Input intent	Precondition	Postcondition
1	MAP_ROUTE_32	warp at 6, 79	walk onto the warp	on Route 32	now in MAP_UNION_CAVE_1F at 17, 3 (warp 4)
2	MAP_UNION_CAVE_1F	-	use MAX_REPEL from the pack	have one	250 steps of encounter suppression
3	MAP_UNION_CAVE_1F	avoid sight lines of UNIONCAVE1F_POKEFAN_M2 (15, 8, sight 3, facing left) and UNIONCAVE1F_FISHER2 (15, 15, sight 2, spinner)	walk south-west	-	EVENT_BEAT_* untouched if avoided; the spinner is not reliably avoidable, budget for the battle
4	MAP_UNION_CAVE_1F	south-west water	press A facing water, or walk into it (TrySurfOW)	Fog Badge + SURF	wPlayerState = PLAYER_SURF
5	MAP_UNION_CAVE_1F	warp 2 at 3, 33	step onto it	-	now in MAP_UNION_CAVE_B1F at 3, 33 (warp 4)
6	MAP_UNION_CAVE_B1F	UNIONCAVEB1F_SUPER_NERD1 at 5, 32 (facing left, sight 3)	walk into the sight line / talk	-	battle Pokemaniac Andrew (2x L24 Marowak); sets EVENT_BEAT_POKEMANIAC_ANDREW, +1440
7	MAP_UNION_CAVE_B1F	surf east along the y~30 water	walk east on water	surfing	reach the eastern shelf
8	MAP_UNION_CAVE_B1F	UNIONCAVEB1F_SUPER_NERD2 at 17, 30 (facing left, sight 3)	walk into the sight line	-	battle Pokemaniac Calvin (L26 Kangaskhan); sets EVENT_BEAT_POKEMANIAC_CALVIN, +1560
9	MAP_UNION_CAVE_B1F	optional item ball 17, 23	press A	EVENT_UNION_CAVE_B1F_X_DEFEND clear	X_DEFEND in bag, flag set
10	MAP_UNION_CAVE_B1F	warp 5 at 17, 31	step onto it	-	now in MAP_UNION_CAVE_B2F at 5, 3; MAPCALLBACK_OBJECTS runs UnionCaveB2FLaprasCallback
11	MAP_UNION_CAVE_B2F	assert UNIONCAVEB2F_LAPRAS is present	read the object list	weekday == FRIDAY and ENGINE_UNION_CAVE_LAPRAS clear	if absent, abort the run - nothing later will fix it
12	MAP_UNION_CAVE_B2F	item ball 16, 2	press A	EVENT_UNION_CAVE_B2F_ELIXER clear	ELIXER in bag (walkthrough omits this one)
13	MAP_UNION_CAVE_B2F	surf south from the entrance shelf	walk south on water	surfing	approach the y~19-23 shelves
14	MAP_UNION_CAVE_B2F	item ball 12, 19 (right-hand shore)	land, press A	EVENT_UNION_CAVE_B2F_HYPER_POTION clear	HYPER_POTION in bag
15	MAP_UNION_CAVE_B2F	UNIONCAVEB2F_ROCKER at 17, 23 (facing left, sight 5 - the longest on the floor)	walk into the sight line	-	battle Cooltrainer Nick (L26 Charmander/Squirtle/Bulbasaur, custom moves); sets EVENT_BEAT_COOLTRAINERM_NICK, +1248
16	MAP_UNION_CAVE_B2F	cross to the left shore, head north to UNIONCAVEB2F_COOLTRAINER_F1 at 5, 13 (spinner, sight 1)	walk adjacent	-	battle Cooltrainer Gwen (L26 Eevee, L22 Flareon/Vaporeon/Jolteon); sets EVENT_BEAT_COOLTRAINERF_GWEN, +1056
17	MAP_UNION_CAVE_B2F	walk the left path south to UNIONCAVEB2F_COOLTRAINER_F2 at 3, 28 (facing down, sight 2)	walk into the sight line	-	battle Cooltrainer Emma (L28 Poliwhirl); sets EVENT_BEAT_COOLTRAINERF_EMMA, +1344
18	MAP_UNION_CAVE_B2F	save	open menu -> SAVE	Lapras still present	recoverable checkpoint
19	MAP_UNION_CAVE_B2F	surf east/south-east from 3, 28 toward 11, 31	walk on water	surfing	the Lapras object drifts within +/-1 cell of 11, 31 (SWIM_WANDER, radius 1,1) - re-scan its live position each step
20	MAP_UNION_CAVE_B2F	press A facing UNIONCAVEB2F_LAPRAS	talk	object present	UnionCaveLapras runs: cry LAPRAS, loadwildmon LAPRAS, 20, startbattle
21	battle	L20 wild Lapras	inflict sleep/paralysis, chip to yellow/red, throw ULTRA_BALLs	-	on any exit: disappear + setflag ENGINE_UNION_CAVE_LAPRAS, then reloadmapafterbattle
22	-	verify Lapras in party/box	read party	-	if not caught, reload the step-18 save; do not walk out and back in, the callback will not re-place it
23	MAP_UNION_CAVE_B2F	use ESCAPE_ROPE	pack -> use	in a cave tileset	back at the last Pokemon Center door

Sight-line arithmetic for steps 6/8/15/16/17: Trainers.sees in the port (src/world/gen2/Trainers.lua:98) is the transcription of home/trainers.asm - the NPC must be facing the player's direction and the Chebyshev-free straight distance must be <= sight.

5. Port coverage

Beat	Port file	Status
Union Cave 1F/B1F/B2F map data (headers, blocks, warps, objects)	src/import/RomExtractorGen2.lua (generic map/manifest extraction; per-map entries land in the private data/generated/ cache)	implemented - data-driven, no per-map code
MAPCALLBACK_OBJECTS dispatch on map load	src/world/gen2/World.lua:5700 (self:runMapCallback("MAPCALLBACK_OBJECTS"), deliberately before the sprite rebuild)	implemented
readvar VAR_WEEKDAY	src/world/gen2/World.lua:101 (VAR_WEEKDAY = 0x0b) and :1222 (if varId == VAR_WEEKDAY then return self:weekday() end)	implemented
checkflag / setflag on ENGINE_*	src/script/gen2/Vm.lua:195 / :208	implemented
ENGINE_UNION_CAVE_LAPRAS as a daily flag	src/core/gen2/Apricorns.lua:84 ({ id = 88, name = "ENGINE_UNION_CAVE_LAPRAS" } in the wDailyFlags1/2 id list) and :344 (save.dailyFlags = {} on the daily wipe)	implemented
appear / disappear object masking	src/script/gen2/Opcodes.lua:115-116, consumed by the World object rebuild	implemented
cry	src/script/gen2/Vm.lua:621	implemented
loadwildmon + startbattle + reloadmapafterbattle (the whole static-encounter shape)	src/script/gen2/Vm.lua:836, :817, :886	implemented
Wild catch rate / Ultra Ball / status bonus	src/battle/gen2/Catching.lua (transcribes PokeBallEffect, including the two cart bugs)	implemented
Water encounter tables while surfing	src/world/gen2/FieldMoves.lua:175 ("standing in a cave rolls the grass list; surfing rolls the water" ...) + src/battle/gen2/Encounter.lua	implemented
Surf gate on ENGINE_FOGBADGE	src/world/gen2/FieldMoves.lua:106 (SURF = "FOG") and FieldMoves.surfFromMenu at :481	implemented
Trainer eyesight approach + battle	src/world/gen2/Trainers.lua:98 (Trainers.sees), src/world/gen2/World.lua:5212 / :5227 / :5242	implemented
Trainer prize money (base x level x 4, Mom's split)	src/battle/gen2/Prize.lua:82 (Prize.reward), :92 (Prize.rewardLevel)	implemented - and it already documents the ld c, 4 that makes the walkthrough's figures right
Repel step counting (the Max Repel advice)	src/world/gen2/World.lua:317 (REPEL_STEPS = { REPEL = 100, SUPER_REPEL = 200, MAX_REPEL = 250 }), :3366	implemented
Item ball pickup (OBJECTTYPE_ITEMBALL, i.e. the B2F Elixer / Hyper Potion and every ball on 1F/B1F)	extractor stores the item at src/import/RomExtractorGen2.lua:2969 (obj.itemball = readItemBall(...)) and deliberately assigns no scriptKey; World:talk only dispatches on npc.def.scriptKey (src/world/gen2/World.lua:5276)	missing - no consumer of obj.itemball exists anywhere under src/. Pressing A on a Poke Ball object currently does nothing
Escape Rope from a cave	src/ui/PartyMenu.lua:634 is the Gen 1 DIG/ESCAPE_ROPE path; no Gen 2 equivalent found under src/core/gen2/ or src/world/gen2/	unverified / likely missing for Gen 2 - a driver should warp out manually
A driver exercising the weekday-gated MAPCALLBACK_OBJECTS shape	tests/drivers/gold_map_callbacks.lua:117-156 covers the same pattern on Route 29 (Tuscany, Tuesday)	implemented for the pattern, not for Union Cave B2F specifically - no tests/drivers/gold_* driver mentions Union Cave or Lapras

Honest summary: everything the Lapras encounter itself needs is in place (callback dispatch, weekday var, daily flags, loadwildmon/startbattle, catching). The two gaps that would bite a bot on this route are item balls are not pickable and no Gen 2 Escape Rope, neither of which blocks Lapras.

6. Unresolved / verify by hand

• "Lapras only appears on Friday" vs. the 1F NPC hints. The code checks exactly FRIDAY (UnionCaveB2FLaprasCallback). But FirebreatherBillAfterBattleText on 1F says "On weekends, you can hear strange roars from deep in the cave" while PokemaniacLarryAfterBattleText says "Every Friday". Larry is right, Bill's line is flavour that contradicts the callback. The walkthrough follows Larry and is correct.
• "once you've gotten HM Surf". The asm imposes no HM/badge check on the Lapras callback or on UnionCaveLapras; Surf is a reachability requirement (B2F's Lapras sits at 11, 31 surrounded by water and the approach legs on 1F/B1F cross water), enforced only by SurfFunction.TrySurf's ENGINE_FOGBADGE check. The walkthrough's phrasing implies a scripted gate that does not exist.
• EXP figures. The walkthrough quotes per-mon EXP (637 for a L24 Marowak, 975 for a L26 Kangaskhan, 355/511/924/928/933/786, and two "?" entries). EXP is computed at runtime from base EXP x level, not stored per trainer, so none of these could be pinned to a table row. They are plausible but unverified here; data/pokemon/base_stats/*.asm would be the place to check.
• Party ordering. The walkthrough lists Nick as Charmander / Bulbasaur / Squirtle and Gwen as Eevee / Vaporeon / Jolteon / Flareon. parties.asm has Nick as Charmander / Squirtle / Bulbasaur (:742) and Gwen as Eevee / Flareon / Vaporeon / Jolteon (:867). The sets match; the order does not. A bot planning lead matchups should use the asm order (it is also what decides the prize level: Gwen's last row is Jolteon L22).
• "Head almost all the way through till you see the guy on the cliff still spinning around, which is the third trainer that you spot." Read against the 1F object table this is UNIONCAVE1F_FISHER2 (Firebreather Bill, 15, 15, SPRITEMOVEDATA_SPINRANDOM_FAST), with Hiker Daniel (4, 4) and Hiker Russell (15, 8) as the first two. That reading is an inference from coordinates and movement data, not something the asm states; the exact walking order depends on the .blk layout, which was not decoded here.
• Which 1F ladder the walkthrough means. "Down and to the left is a lake. Surf past it and head down the ladder" is read as 1F warp 2 (3, 33 -> UNION_CAVE_B1F warp 4 at 3, 33), because Andrew stands at B1F 5, 32, immediately beside that arrival point. 1F warp 1 (5, 19 -> B1F warp 3 at 7, 19) would land nowhere near him. Verify against the block layout if a driver's pathing disagrees.
• B2F "right side" / "left side" landings. The prose distinguishes a right and a left shore; the object coordinates (12, 19 Hyper Potion and 17, 23 Nick on the right, 5, 13 Gwen and 3, 28 Emma on the left) are consistent with that, but the actual water/land split comes from UnionCaveB2F.blk, which was not decoded.
• Elixer at B2F 16, 2. Present in the asm, absent from the walkthrough. Not a contradiction, just an omission worth picking up.