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pokecrystal/docs/bugs_and_glitches.md

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Bugs and Glitches

Contents

Thick Club and Light Ball can decrease damage done with boosted (Special) Attack

(Video)

This is a bug with SpeciesItemBoost in battle/effect_commands.asm:

; Double the stat
	sla l
	rl h
	ret

Fix:

; Double the stat
	sla l
	rl h

	ld a, 999 / $100
	cp h
	jr c, .cap
	ld a, 999 % $100
	cp l
	ret nc

.cap
	ld h, 999 / $100
	ld l, 999 % $100
	ret

Metal Powder can increase damage taken with boosted (Special) Defense

(Video)

This is a bug with DittoMetalPowder in battle/effect_commands.asm:

	ld a, c
	srl a
	add c
	ld c, a
	ret nc

	srl b
	ld a, b
	and a
	jr nz, .done
	inc b
.done
	scf
	rr c
	ret

Fix:

	ld a, c
	srl a
	add c
	ld c, a
	ret nc

	srl b
	ld a, b
	and a
	jr nz, .done
	inc b
.done
	scf
	rr c

	ld a, 999 / $100
	cp b
	jr c, .cap
	ld a, 999 % $100
	cp c
	ret nc

.cap
	ld b, 999 / $100
	ld c, 999 % $100
	ret

Belly Drum sharply boosts Attack even with under 50% HP

(Video)

This is a bug with BattleCommand_BellyDrum in battle/effect_commands.asm:

BattleCommand_BellyDrum: ; 37c1a
; bellydrum
; This command is buggy because it raises the user's attack
; before checking that it has enough HP to use the move.
; Swap the order of these two blocks to fix.
	call BattleCommand_AttackUp2
	ld a, [AttackMissed]
	and a
	jr nz, .failed

	callab GetHalfMaxHP
	callab CheckUserHasEnoughHP
	jr nc, .failed

Fix:

BattleCommand_BellyDrum: ; 37c1a
; bellydrum
	callab GetHalfMaxHP
	callab CheckUserHasEnoughHP
	jr nc, .failed

	call BattleCommand_AttackUp2
	ld a, [AttackMissed]
	and a
	jr nz, .failed

HP bar animation is slow for high HP

(Video)

This is a bug with LongAnim_UpdateVariables in engine/anim_hp_bar.asm:

	; This routine is buggy. The result from ComputeHPBarPixels is stored
	; in e. However, the pop de opcode deletes this result before it is even
	; used. The game then proceeds as though it never deleted that output.
	; To fix, uncomment the line below.
	call ComputeHPBarPixels
	; ld a, e
	pop bc
	pop de
	pop hl
	ld a, e ; Comment or delete this line to fix the above bug.
	ld hl, wCurHPBarPixels
	cp [hl]
	jr z, .loop
	ld [hl], a
	and a
	ret

Fix: Move ld a, e to right after call ComputeHPBarPixels.

HP bar animation off-by-one error for low HP

(Video)

This is a bug with ShortHPBar_CalcPixelFrame in engine/anim_hp_bar.asm:

	ld b, 0
; This routine is buggy. If [wCurHPAnimMaxHP] * [wCurHPBarPixels] is divisible
; by 48, the loop runs one extra time. To fix, uncomment the line below.
.loop
	ld a, l
	sub 6 * 8
	ld l, a
	ld a, h
	sbc $0
	ld h, a
	; jr z, .done
	jr c, .done
	inc b
	jr .loop

Fix: Uncomment jr z, .done.

Experience underflow for level 1 Pokémon with Medium-Slow growth rate

(Video)

This can bring Pokémon straight from level 1 to 100 by gaining just a few experience points.

This is a bug with CalcExpAtLevel in main.asm:

CalcExpAtLevel: ; 50e47
; (a/b)*n**3 + c*n**2 + d*n - e
	ld a, [BaseGrowthRate]
	add a
	add a
	ld c, a
	ld b, 0
	ld hl, GrowthRates
	add hl, bc

Fix:

CalcExpAtLevel: ; 50e47
; (a/b)*n**3 + c*n**2 + d*n - e
	ld a, d
	cp 1
	jr nz, .UseExpFormula
; Pokémon have 0 experience at level 1
	xor a
	ld hl, hProduct
	ld [hli], a
	ld [hli], a
	ld [hli], a
	ld [hl], a
	ret

.UseExpFormula
	ld a, [BaseGrowthRate]
	add a
	add a
	ld c, a
	ld b, 0
	ld hl, GrowthRates
	add hl, bc

Five-digit experience gain is printed incorrectly

(Video)

This is a bug with Text_ABoostedStringBuffer2ExpPoints and Text_StringBuffer2ExpPoints in text/common_2.asm:

Text_ABoostedStringBuffer2ExpPoints::
	text ""
	line "a boosted"
	cont "@"
	deciram StringBuffer2, 2, 4
	text " EXP. Points!"
	prompt

Text_StringBuffer2ExpPoints::
	text ""
	line "@"
	deciram StringBuffer2, 2, 4
	text " EXP. Points!"
	prompt

Fix: Change both deciram StringBuffer2, 2, 4 to deciram StringBuffer2, 2, 5.

NPC use of Full Heal or Full Restore does not cure Nightmare status

(Video)

This is a bug with AI_HealStatus in battle/ai/items.asm:

AI_HealStatus: ; 384e0
	ld a, [CurOTMon]
	ld hl, OTPartyMon1Status
	ld bc, PARTYMON_STRUCT_LENGTH
	call AddNTimes
	xor a
	ld [hl], a
	ld [EnemyMonStatus], a
	; Bug: this should reset SUBSTATUS_NIGHTMARE too
	; Uncomment the lines below to fix
	; ld hl, EnemySubStatus1
	; res SUBSTATUS_NIGHTMARE, [hl]
	ld hl, EnemySubStatus5
	res SUBSTATUS_TOXIC, [hl]
	ret
; 384f7

Fix: Uncomment ld hl, EnemySubStatus1 and res SUBSTATUS_NIGHTMARE, [hl].

"Smart" AI encourages Mean Look if its own Pokémon is badly poisoned

(Video)

This is a bug with AI_Smart_MeanLook in battle/ai/scoring.asm:

; 80% chance to greatly encourage this move if the enemy is badly poisoned (buggy).
; Should check PlayerSubStatus5 instead.
	ld a, [EnemySubStatus5]
	bit SUBSTATUS_TOXIC, a
	jr nz, .asm_38e26

Fix: Change EnemySubStatus5 to PlayerSubStatus5.

A Disabled, PP Up–enhanced move may not trigger automatic Struggling

(Video)

This is a bug with CheckPlayerHasUsableMoves in battle/core.asm:

.done
	; Bug: this will result in a move with PP Up confusing the game.
	; Replace with "and $3f" to fix.
	and a
	ret nz

.force_struggle
	ld hl, BattleText_PkmnHasNoMovesLeft
	call StdBattleTextBox
	ld c, 60
	call DelayFrames
	xor a
	ret

Fix: Change and a to and $3f.

Counter and Mirror Coat still work if the opponent uses an item

(Video)

To do: Identify specific code causing this bug and fix it.

Present damage is incorrect in link battles

(Video)

This bug existed for all battles in Gold and Silver, and was only fixed for single-player battles in Crystal to preserve link compatibility.

This is a bug with BattleCommand_Present in battle/effects/present.asm:

BattleCommand_Present: ; 37874
; present

	ld a, [wLinkMode]
	cp LINK_COLOSSEUM
	jr z, .colosseum_skippush
	push bc
	push de
.colosseum_skippush

	call BattleCommand_Stab

	ld a, [wLinkMode]
	cp LINK_COLOSSEUM
	jr z, .colosseum_skippop
	pop de
	pop bc
.colosseum_skippop

Fix:

BattleCommand_Present: ; 37874
; present

	push bc
	push de
	call BattleCommand_Stab
	pop de
	pop bc

BRN/PSN/PAR do not affect catch rate

This is a bug with PokeBall in items/item_effects.asm:

.statuscheck
; This routine is buggy. It was intended that SLP and FRZ provide a higher
; catch rate than BRN/PSN/PAR, which in turn provide a higher catch rate than
; no status effect at all. But instead, it makes BRN/PSN/PAR provide no
; benefit.
; Uncomment the line below to fix this.
	ld b, a
	ld a, [EnemyMonStatus]
	and 1 << FRZ | SLP
	ld c, 10
	jr nz, .addstatus
	; ld a, [EnemyMonStatus]
	and a
	ld c, 5
	jr nz, .addstatus
	ld c, 0
.addstatus
	ld a, b
	add c
	jr nc, .max_1
	ld a, $ff
.max_1

Fix: Uncomment ld a, [EnemyMonStatus].

Moon Ball does not boost catch rate

This is a bug with MoonBallMultiplier in items/item_effects.asm:

MoonBallMultiplier:
; This function is buggy.
; Intent:  multiply catch rate by 4 if mon evolves with moon stone
; Reality: no boost

...

; Moon Stone's constant from Pokémon Red is used.
; No Pokémon evolve with Burn Heal,
; so Moon Balls always have a catch rate of 1×.
	push bc
	ld a, BANK(EvosAttacks)
	call GetFarByte
	cp MOON_STONE_RED ; BURN_HEAL
	pop bc
	ret nz

Fix: Change MOON_STONE_RED to MOON_STONE.

Love Ball boosts catch rate for the wrong gender

This is a bug with LoveBallMultiplier in items/item_effects.asm:

LoveBallMultiplier:
; This function is buggy.
; Intent:  multiply catch rate by 8 if mons are of same species, different sex
; Reality: multiply catch rate by 8 if mons are of same species, same sex

...

	ld a, d
	pop de
	cp d
	pop bc
	ret nz ; for the intended effect, this should be "ret z"

Fix: Change ret nz to ret z.

Fast Ball only boosts catch rate for three Pokémon

This is a bug with FastBallMultiplier in items/item_effects.asm:

FastBallMultiplier:
; This function is buggy.
; Intent:  multiply catch rate by 4 if enemy mon is in one of the three
;          FleeMons tables.
; Reality: multiply catch rate by 4 if enemy mon is one of the first three in
;          the first FleeMons table.

...

	inc hl
	cp -1
	jr z, .next
	cp c
	jr nz, .next ; for the intended effect, this should be "jr nz, .loop"
	sla b
	jr c, .max

Fix: Change jr nz, .next to jr nz, .loop.

Friend Ball catches sent to the PC overwrite the wrong Pokémon's happiness

This is a bug with PokeBall in items/item_effects.asm:

	ld a, [CurItem]
	cp FRIEND_BALL
	jr nz, .SkipBoxMonFriendBall
	; Bug: overwrites the happiness of the first mon in the box!
	ld a, FRIEND_BALL_HAPPINESS
	ld [sBoxMon1Happiness], a
.SkipBoxMonFriendBall:

sBoxMon1Happiness is written before the Friend Ball Pokémon is deposited.

Dragon Scale, not Dragon Fang, boosts Dragon-type moves

This is a bug with ItemAttributes in items/item_attributes.asm:

; DRAGON FANG
	item_attribute 100, 0, 0, CANT_SELECT, ITEM, ITEMMENU_NOUSE, ITEMMENU_NOUSE

...

; DRAGON SCALE
	item_attribute 2100, HELD_DRAGON_BOOST, 10, CANT_SELECT, ITEM, ITEMMENU_NOUSE, ITEMMENU_NOUSE

Fix: Move HELD_DRAGON_BOOST to the DRAGON FANG attributes and 0 to DRAGON SCALE.

Daisy's massages don't always increase happiness

This is a bug with MassageOrHaircut in event/special.asm:

; Bug: Subtracting $ff from $ff fails to set c.
; This can result in overflow into the next data array.
; In the case of getting a massage from Daisy, we bleed
; into CopyPokemonName_Buffer1_Buffer3, which passes
; $d0 to ChangeHappiness and returns $73 to the script.
; The end result is that there is a 0.4% chance your
; Pokemon's happiness will not change at all.
.loop
	sub [hl]
	jr c, .ok
	inc hl
	inc hl
	inc hl
	jr .loop

.ok
	inc hl
	ld a, [hli]
	ld [ScriptVar], a
	ld c, [hl]
	call ChangeHappiness
	ret

...

Data_DaisyMassage: ; 746b
	db $ff, 2, HAPPINESS_MASSAGE ; 99.6% chance

CopyPokemonName_Buffer1_Buffer3: ; 746e
	ld hl, StringBuffer1
	ld de, StringBuffer3
	ld bc, PKMN_NAME_LENGTH
	jp CopyBytes

Fix:

Data_DaisyMassage: ; 746b
	db $80, 2, HAPPINESS_MASSAGE ; 50% chance
	db $ff, 2, HAPPINESS_MASSAGE ; 50% chance

Magikarp in Lake of Rage are shorter, not longer

This is a bug with LoadEnemyMon.CheckMagikarpArea in battle/core.asm:

.CheckMagikarpArea:
; The z checks are supposed to be nz
; Instead, all maps in GROUP_LAKE_OF_RAGE (mahogany area)
; and routes 20 and 44 are treated as Lake of Rage

; This also means Lake of Rage Magikarp can be smaller than ones
; caught elsewhere rather than the other way around

; Intended behavior enforces a minimum size at Lake of Rage
; The real behavior prevents size flooring in the Lake of Rage area
	ld a, [MapGroup]
	cp GROUP_LAKE_OF_RAGE
	jr z, .Happiness
	ld a, [MapNumber]
	cp MAP_LAKE_OF_RAGE
	jr z, .Happiness

Fix: Change both jr z, .Happiness to jr nz, .Happiness.

Battle transitions fail to account for the enemy's level

(Video)

This is a bug with StartTrainerBattle_DetermineWhichAnimation in engine/battle_start.asm:

StartTrainerBattle_DetermineWhichAnimation: ; 8c365 (23:4365)
; The screen flashes a different number of times depending on the level of
; your lead Pokemon relative to the opponent's.
; BUG: BattleMonLevel and EnemyMonLevel are not set at this point, so whatever
; values happen to be there will determine the animation.
	ld de, 0
	ld a, [BattleMonLevel]
	add 3
	ld hl, EnemyMonLevel
	cp [hl]
	jr nc, .okay
	set 0, e
.okay
	ld a, [wPermission]
	cp CAVE
	jr z, .okay2
	cp PERM_5
	jr z, .okay2
	cp DUNGEON
	jr z, .okay2
	set 1, e
.okay2
	ld hl, .StartingPoints
	add hl, de
	ld a, [hl]
	ld [wJumptableIndex], a
	ret
; 8c38f (23:438f)

.StartingPoints: ; 8c38f
	db 1,  9
	db 16, 24
; 8c393

To do: Fix this bug.

No bump noise if standing on tile $3E

This is a bug with DoPlayerMovement.CheckWarp in engine/player_movement.asm:

; Bug: Since no case is made for STANDING here, it will check
; [.edgewarps + $ff]. This resolves to $3e at $8035a.
; This causes wd041 to be nonzero when standing on tile $3e,
; making bumps silent.

	ld a, [WalkingDirection]
	ld e, a
	ld d, 0
	ld hl, .EdgeWarps
	add hl, de
	ld a, [PlayerStandingTile]
	cp [hl]
	jr nz, .not_warp

	ld a, 1
	ld [wd041], a
	ld a, [WalkingDirection]
	cp STANDING
	jr z, .not_warp

Fix:

	ld a, [WalkingDirection]
	cp STANDING
	jr z, .not_warp
	ld e, a
	ld d, 0
	ld hl, .EdgeWarps
	add hl, de
	ld a, [PlayerStandingTile]
	cp [hl]
	jr nz, .not_warp

	ld a, 1
	ld [wd041], a
	ld a, [WalkingDirection]

LoadMetatiles wrap around past 128 blocks

home/map.asm:

	; Set hl to the address of the current metatile data ([TilesetBlocksAddress] + (a) tiles).
	; This is buggy; it wraps around past 128 blocks.
	; To fix, uncomment the line below.
	add a ; Comment or delete this line to fix the above bug.
	ld l, a
	ld h, 0
	; add hl, hl
	add hl, hl
	add hl, hl
	add hl, hl
	ld a, [TilesetBlocksAddress]
	add l
	ld l, a
	ld a, [TilesetBlocksAddress + 1]
	adc h
	ld h, a

Fix: Delete add a and uncomment add hl, hl.

Surfing directly across a map connection does not load the new map

(Video)

To do: Identify specific code causing this bug and fix it.

CheckOwnMon only checks the first five letters of OT names

(Video)

This bug can allow you to talk to Eusine in Celadon City and encounter Ho-Oh with only traded legendary beasts.

engine/search.asm:

; check OT
; This only checks five characters, which is fine for the Japanese version,
; but in the English version the player name is 7 characters, so this is wrong.

	ld hl, PlayerName

rept NAME_LENGTH_JAPANESE +- 2 ; should be PLAYER_NAME_LENGTH +- 2
	ld a, [de]
	cp [hl]
	jr nz, .notfound
	cp "@"
	jr z, .found ; reached end of string
	inc hl
	inc de
endr

	ld a, [de]
	cp [hl]
	jr z, .found

.notfound
	pop de
	pop hl
	pop bc
	and a
	ret

Fix: Change rept NAME_LENGTH_JAPANESE +- 2 to rept PLAYER_NAME_LENGTH +- 2.

HELD_CATCH_CHANCE has no effect

This is a bug with PokeBall in items/item_effects.asm:

	; BUG: callba overwrites a,
	; and GetItemHeldEffect takes b anyway.

	; This is probably the reason
	; the HELD_CATCH_CHANCE effect
	; is never used.

	; Uncomment the line below to fix.

	ld a, [BattleMonItem]
;	ld b, a
	callba GetItemHeldEffect
	ld a, b
	cp HELD_CATCH_CHANCE

Fix: Uncomment ld b, a.

ScriptCall can overflow wScriptStack and crash

engine/scripting.asm:

ScriptCall:
; Bug: The script stack has a capacity of 5 scripts, yet there is
; nothing to stop you from pushing a sixth script.  The high part
; of the script address can then be overwritten by modifications
; to ScriptDelay, causing the script to return to the rst/interrupt
; space.

	push de
	ld hl, wScriptStackSize
	ld e, [hl]
	inc [hl]
	ld d, $0
	ld hl, wScriptStack
	add hl, de
	add hl, de
	add hl, de
	pop de
	ld a, [ScriptBank]
	ld [hli], a
	ld a, [ScriptPos]
	ld [hli], a
	ld a, [ScriptPos + 1]
	ld [hl], a
	ld a, b
	ld [ScriptBank], a
	ld a, e
	ld [ScriptPos], a
	ld a, d
	ld [ScriptPos + 1], a
	ret

LoadSpriteGFX does not limit the capacity of UsedSprites

engine/overworld.asm:

LoadSpriteGFX: ; 14306
; Bug: b is not preserved, so
; it's useless as a next count.

	ld hl, UsedSprites
	ld b, SPRITE_GFX_LIST_CAPACITY
.loop
	ld a, [hli]
	and a
	jr z, .done
	push hl
	call .LoadSprite
	pop hl
	ld [hli], a
	dec b
	jr nz, .loop

.done
	ret

.LoadSprite:
	call GetSprite
	ld a, l
	ret
; 1431e

GetSprite modifies b. Surround it with push bc/pop bc to fix.

ChooseWildEncounter doesn't really validate the wild Pokémon species

engine/wildmons.asm:

ChooseWildEncounter: ; 2a14f
...

	ld a, b
	ld [CurPartyLevel], a
	ld b, [hl]
	; ld a, b
	call ValidateTempWildMonSpecies
	jr c, .nowildbattle

	ld a, b ; This is in the wrong place.
	cp UNOWN
	jr nz, .done

...

ValidateTempWildMonSpecies: ; 2a4a0
; Due to a development oversight, this function is called with the wild Pokemon's level, not its species, in a.

Fix:

	ld a, b
	ld [CurPartyLevel], a
	ld b, [hl]
	ld a, b
	call ValidateTempWildMonSpecies
	jr c, .nowildbattle

	cp UNOWN
	jr nz, .done

TryObjectEvent arbitrary code execution

engine/events.asm:

; Bug: If IsInArray returns nc, data at bc will be executed as code.
	push bc
	ld de, 3
	ld hl, .pointers
	call IsInArray
	jr nc, .nope_bugged
	pop bc

	inc hl
	ld a, [hli]
	ld h, [hl]
	ld l, a
	jp hl

.nope_bugged
	; pop bc
	xor a
	ret

Fix: Uncomment pop bc.

Special_CheckBugContestContestantFlag can read beyond its data table

event/bug_contest_2.asm:

Special_CheckBugContestContestantFlag: ; 139ed
; Checks the flag of the Bug Catching Contestant whose index is loaded in a.

; Bug: If a >= 10 when this is called, it will read beyond the table.

	ld hl, BugCatchingContestantEventFlagTable
	ld e, a
	ld d, 0
	add hl, de
	add hl, de
	ld e, [hl]
	inc hl
	ld d, [hl]
	ld b, CHECK_FLAG
	call EventFlagAction
	ret
; 139fe

BugCatchingContestantEventFlagTable: ; 139fe
	dw EVENT_BUG_CATCHING_CONTESTANT_1A
	dw EVENT_BUG_CATCHING_CONTESTANT_2A
	dw EVENT_BUG_CATCHING_CONTESTANT_3A
	dw EVENT_BUG_CATCHING_CONTESTANT_4A
	dw EVENT_BUG_CATCHING_CONTESTANT_5A
	dw EVENT_BUG_CATCHING_CONTESTANT_6A
	dw EVENT_BUG_CATCHING_CONTESTANT_7A
	dw EVENT_BUG_CATCHING_CONTESTANT_8A
	dw EVENT_BUG_CATCHING_CONTESTANT_9A
	dw EVENT_BUG_CATCHING_CONTESTANT_10A
; 13a12

ClearWRAM only clears WRAM bank 1

home/init.asm:

ClearWRAM:: ; 25a
; Wipe swappable WRAM banks (1-7)
; Assumes CGB or AGB

	ld a, 1
.bank_loop
	push af
	ld [rSVBK], a
	xor a
	ld hl, $d000
	ld bc, $1000
	call ByteFill
	pop af
	inc a
	cp 8
	jr nc, .bank_loop ; Should be jr c
	ret
; 270

Fix: Change jr nc, .bank_loop to jr c, .bank_loop.

GetForestTreeFrame works, but it's still bad

tilesets/animations.asm:

GetForestTreeFrame: ; fc54c
; Return 0 if a is even, or 2 if odd.
	and a
	jr z, .even
	cp 1
	jr z, .odd
	cp 2
	jr z, .even
	cp 3
	jr z, .odd
	cp 4
	jr z, .even
	cp 5
	jr z, .odd
	cp 6
	jr z, .even
.odd
	ld a, 2
	scf
	ret
.even
	xor a
	ret
; fc56d

Fix:

GetForestTreeFrame: ; fc54c
; Return 0 if a is even, or 2 if odd.
	and 1
	add a
	ret
; fc56d