# Bugs and Glitches ## Thick Club and Light Ball can decrease damage done with boosted (Special) Attack ([Video](https://www.youtube.com/watch?v=rGqu3d3pdok&t=450)) This is a bug with `SpeciesItemBoost` in [battle/effect_commands.asm](battle/effect_commands.asm): ```asm ; Double the stat sla l rl h ret ``` **Fix:** ```asm ; 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](https://www.youtube.com/watch?v=rGqu3d3pdok&t=450)) This is a bug with `DittoMetalPowder` in [battle/effect_commands.asm](battle/effect_commands.asm): ```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:** ```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 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](https://www.youtube.com/watch?v=zuCLMikWo4Y)) This is a bug with `BattleCommand_BellyDrum` in [battle/effect_commands.asm](battle/effect_commands.asm): ```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:** ```asm 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](https://www.youtube.com/watch?v=SE-BfsFgZVM)) This is a bug with `LongAnim_UpdateVariables` in [engine/anim_hp_bar.asm](engine/anim_hp_bar.asm): ```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](https://www.youtube.com/watch?v=9KyNVIZxJvI)) This is a bug with `ShortHPBar_CalcPixelFrame` in [engine/anim_hp_bar.asm](engine/anim_hp_bar.asm): ```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](https://www.youtube.com/watch?v=SXH8u0plHrE)) 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](main.asm): ```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:** ```asm 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](https://www.youtube.com/watch?v=o54VjpAEoO8)) This is a bug with `Text_ABoostedStringBuffer2ExpPoints` and `Text_StringBuffer2ExpPoints` in [text/common_2.asm](text/common_2.asm): ```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](https://www.youtube.com/watch?v=rGqu3d3pdok&t=322) This is a bug with `AI_HealStatus` in [battle/ai/items.asm](battle/ai/items.asm): ```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](https://www.youtube.com/watch?v=cygMO-zHTls)) This is a bug with `AI_Smart_MeanLook` in [battle/ai/scoring.asm](battle/ai/scoring.asm): ```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](https://www.youtube.com/watch?v=1v9x4SgMggs)) This is a bug with `CheckPlayerHasUsableMoves` in [battle/core.asm](battle/core.asm): ```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](https://www.youtube.com/watch?v=uRYyzKRatFk)) *To do:* Identify specific code causing this bug and fix it. ## Present damage is incorrect in link battles ([Video](https://www.youtube.com/watch?v=XJaQoKtrEuw)) 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](battle/effects/present.asm): ```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:** ```asm 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](items/item_effects.asm): ```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](items/item_effects.asm): ```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](items/item_effects.asm): ```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](items/item_effects.asm): ```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](items/item_effects.asm): ```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](items/item_attributes.asm): ```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](event/special.asm): ```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:** ```asm 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](battle/core.asm): ```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](https://www.youtube.com/watch?v=eij_1060SMc)) This is a bug with `StartTrainerBattle_DetermineWhichAnimation` in [engine/battle_start.asm](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](engine/player_movement.asm): ```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:** ```asm 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] ``` ## Surfing directly across a map connection does not load the new map ([Video](https://www.youtube.com/watch?v=XFOWvMNG-zw)) *To do:* Identify specific code causing this bug and fix it. ## `CheckOwnMon` only checks the first five letters of OT names ([Video](https://www.youtube.com/watch?v=GVTTmReM4nQ)) This bug can allow you to talk to Eusine in Celadon City and encounter Ho-Oh with only traded legendary beasts. [engine/search.asm](engine/search.asm): ```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](items/item_effects.asm): ```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](engine/scripting.asm): ```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](engine/overworld.asm): ```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](engine/wildmons.asm): ```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:** ```asm 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](engine/events.asm): ```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](event/bug_contest_2.asm): ```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](home/init.asm): ```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](tilesets/animations.asm): ```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:** ```asm GetForestTreeFrame: ; fc54c ; Return 0 if a is even, or 2 if odd. and 1 add a ret ; fc56d ```