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Add a new Pokémon
This tutorial is for how to add a new species of Pokémon, allowing up to 253 species. As an example, we'll add Munchlax.
- Define a species constant
- Give it a name
- Define its base data
- Define its evolutions and level-up learnset
- Define its egg moves
- Define its cry
- Define its icon
- Define its Pokédex entry
- Design its footprint
- Design its sprites and animation
- Include and point to the sprite and animation data
- Adding up to 253 Pokémon
1. Define a species constant
; pokemon ids ; indexes for: ; - PokemonNames (see data/pokemon/names.asm) ; - BaseData (see data/pokemon/base_stats.asm) ; - EvosAttacksPointers (see data/pokemon/evos_attacks_pointers.asm) ; - EggMovePointers (see data/pokemon/egg_move_pointers.asm) ; - PokemonCries (see data/pokemon/cries.asm) ; - MonMenuIcons (see data/pokemon/menu_icons.asm) ; - PokemonPicPointers (see data/pokemon/pic_pointers.asm) ; - PokemonPalettes (see data/pokemon/palettes.asm) ; - PokedexDataPointerTable (see data/pokemon/dex_entry_pointers.asm) ; - AlphabeticalPokedexOrder (see data/pokemon/dex_order_alpha.asm) ; - EZChat_SortedPokemon (see data/pokemon/ezchat_order.asm) ; - NewPokedexOrder (see data/pokemon/dex_order_new.asm) ; - Pokered_MonIndices (see data/pokemon/gen1_order.asm) ; - AnimationPointers (see gfx/pokemon/anim_pointers.asm) ; - AnimationIdlePointers (see gfx/pokemon/idle_pointers.asm) ; - BitmasksPointers (see gfx/pokemon/bitmask_pointers.asm) ; - FramesPointers (see gfx/pokemon/frame_pointers.asm) ; - Footprints (see gfx/footprints.asm) const_def 1 const BULBASAUR ; 01 ... const MEW ; 97 JOHTO_POKEMON EQU const_value const CHIKORITA ; 98 ... const CELEBI ; fb + const MUNCHLAX ; fc NUM_POKEMON EQU const_value + -1 - const MON_FC ; fc const EGG ; fd const MON_FE ; fe
Some things to notice here:
- Species constants are in national dex order; in fact, they're used as Pokédex IDs, so Munchlax is going to appear as #252.
JOHTO_POKEMONis defined right before the first Johto Pokémon, and
NUM_POKEMONis defined right after the last non-Egg Pokémon.
- There are a lot of data tables associated with Pokémon species! We'll go over them one by one.
2. Give it a name
PokemonNames:: db "BULBASAUR@" ... db "CELEBI@@@@" - db "?????@@@@@" + db "MUNCHLAX@@" db "EGG@@@@@@@" db "?????@@@@@" db "?????@@@@@" db "?????@@@@@"
All the names are exactly 10 characters long, with "@" as padding. Names that are 10 characters long anyway, like "CHARMELEON", don't have any padding.
(Aside: if you make names lowercase, be careful—going from "FARFETCH'D" to "Farfetch'd" will lower the character count by 1 since "'d" is a single character, so that would need to become "Farfetch'd@".)
3. Define its base data
Create data/pokemon/base_stats/munchlax.asm; you can start with data/pokemon/base_stats/snorlax.asm as a guide.
There's a lot of base data here:
+ db MUNCHLAX ; 252 + + db 135, 85, 40, 5, 40, 85 + ; hp atk def spd sat sdf + + db NORMAL, NORMAL ; type + db 50 ; catch rate + db 94 ; base exp + db LEFTOVERS, LEFTOVERS ; items + db GENDER_F12_5 ; gender ratio + db 100 ; unknown 1 + db 40 ; step cycles to hatch + db 5 ; unknown 2 + INCBIN "gfx/pokemon/munchlax/front.dimensions" + db 0, 0, 0, 0 ; padding + db GROWTH_SLOW ; growth rate + dn EGG_NONE, EGG_NONE ; egg groups + + ; tm/hm learnset + tmhm DYNAMICPUNCH, HEADBUTT, CURSE, ROLLOUT, TOXIC, ZAP_CANNON, ROCK_SMASH, PSYCH_UP, HIDDEN_POWER, SUNNY_DAY, SNORE, BLIZZARD, HYPER_BEAM, ICY_WIND, PROTECT, RAIN_DANCE, ENDURE, FRUSTRATION, SOLARBEAM, THUNDER, EARTHQUAKE, RETURN, PSYCHIC_M, SHADOW_BALL, MUD_SLAP, DOUBLE_TEAM, ICE_PUNCH, SWAGGER, SLEEP_TALK, SANDSTORM, FIRE_BLAST, DEFENSE_CURL, THUNDERPUNCH, REST, ATTRACT, FIRE_PUNCH, SURF, STRENGTH, FLAMETHROWER, THUNDERBOLT, ICE_BEAM + ; end
From top to bottom, what it all means:
- species: This is just used for declaring which ROM bank the Pokédex entry is stored it. It's arguably a design flaw, since the exact species ID is insignificant, but it's not a big deal; just put the correct species here and move on.
- base stats: HP, Attack, Defense, Speed, Special Attack, and Special Defense, each from 1 to 255.
- type: The primary and secondary types. Single-type Pokémon just repeat their type twice.
- catch rate: A factor in the formula for capturing wild Pokémon. Lower rates are harder to capture. The highest value, 255, is used for common Pokémon like Hoothoot and Rattata; legendaries like Mewtwo and Ho-Oh get as low as 3.
base experience yield: A factor in the formula for awarding experience. Higher values give more experience. As usual, since this is a single byte (
db), its maximum is 255. (Chansey and Blissey both have 255 base exp.)
- items: A common item (23% chance) and a rare item (2% chance) that might be held by this Pokémon in the wild.
gender ratio: The likelihood that an Egg of this Pokémon will be female. Lower values are more likely to be male, with 0 being 100% male, 254 being 100% female, and 255 being genderless (like Magnemite or Staryu). There are named constants for the few values that get officially used:
GENDER_F0: 100% male
GENDER_F12_5: 7/8 male, 1/8 female
GENDER_F25: 3/4 male, 1/4 female
GENDER_F50: 1/2 male, 1/2 female
GENDER_F75: 1/4 male, 3/4 female
GENDER_F100: 100% female
- unknown 1: An unused value that's always 100.
- step cycles to hatch: How many step cycles it takes for an Egg of this Pokémon to hatch. Each step cycle is 256 steps long.
- unknown 2: An unused value that's always 5.
- front.dimensions: The size of the Pokémon's front sprite. The front.dimensions file contains a single byte that's one of three valid values: $55 for a 40x40-pixel (5x5-tile) sprite, $66 for 48x48 pixels (6x6 tiles), or $77 for 56x56 pixels (7x7 tiles). It's automatically generated from the front.png sprite image (we'll get to this later).
- padding: Four unused bytes that are always 0s.
growth rate: The formula that's used to determine experience point thresholds for reaching each level. (The formula coefficients are defined in data/growth_rates.asm.) Valid values:
GROWTH_MEDIUM_FAST: exp = L³ (1,000,000 exp = level 100)
GROWTH_SLIGHTLY_FAST: exp = (3/4)L³ + 10L² − 30 (849,970 exp = level 100); unused
GROWTH_SLIGHTLY_SLOW: exp = (3/4)L³ + 20L² − 70 (949,930 exp = level 100); unused
GROWTH_MEDIUM_SLOW: exp = (6/5)L³ − 15L² + 100L − 140 (1,059,860 exp = level 100)
GROWTH_FAST: exp = (4/5)L³ (800,000 exp = level 100)
GROWTH_SLOW: exp = (5/4)L³ (1,250,000 exp = level 100)
egg groups: The two egg groups this Pokémon is in. Two Pokémon have to share an Egg group to breed. The 15 valid Egg groups (including
EGG_NONEfor sterile Pokémon like babies and legendaries) are defined in constants/pokemon_data_constants.asm.
TM/HM learnset: A list of which TMs, HMs, and tutor moves this Pokémon can learn, passed to the
tmhmmacro. Valid values are defined in constants/item_constants.asm with the
Then edit data/pokemon/base_stats.asm:
BaseData:: INCLUDE "data/pokemon/base_stats/bulbasaur.asm" ... INCLUDE "data/pokemon/base_stats/celebi.asm" +INCLUDE "data/pokemon/base_stats/munchlax.asm"
4. Define its evolutions and level-up learnset
EvosAttacksPointers:: dw BulbasaurEvosAttacks ... dw CelebiEvosAttacks + dw MunchlaxEvosAttacks
Then edit data/pokemon/evos_attacks.asm:
+MunchlaxEvosAttacks: + db EVOLVE_HAPPINESS, TR_ANYTIME, SNORLAX + db 0 ; no more evolutions + db 1, TACKLE + db 1, METRONOME + db 8, AMNESIA + db 15, DEFENSE_CURL + db 22, BELLY_DRUM + db 29, HEADBUTT + db 36, SCREECH + db 36, REST + db 43, BODY_SLAM + db 50, ROLLOUT + db 57, HYPER_BEAM + db 0 ; no more level-up moves
The comment at the top of evos_attacks.asm explains the data structure:
EvosAttacks:: ; Evos+attacks data structure: ; - Evolution methods: ; * db EVOLVE_LEVEL, level, species ; * db EVOLVE_ITEM, used item, species ; * db EVOLVE_TRADE, held item (or -1 for none), species ; * db EVOLVE_HAPPINESS, TR_* constant (ANYTIME, MORNDAY, NITE), species ; * db EVOLVE_STAT, level, ATK_*_DEF constant (LT, GT, EQ), species ; - db 0 ; no more evolutions ; - Learnset (in increasing level order): ; * db level, move ; - db 0 ; no more level-up moves
Munchlax evolves into Snorlax through happiness; and its level-up moves are copied from Snorlax, with a couple replacements (Metronome and Screech).
Note that the order of the
EvosAttacksPointers matters, since the entries pair up with the species constants, but the
EvosAttacks data is unordered. I just put Munchlax's data at the end of the file.
5. Define its egg moves
EggMovePointers:: dw BulbasaurEggMoves ... dw AerodactylEggMoves - dw SnorlaxEggMoves + dw NoEggMoves dw NoEggMoves ... dw NoEggMoves + dw MunchlaxEggMoves
Then edit data/pokemon/egg_moves.asm:
-SnorlaxEggMoves: +MunchlaxEggMoves: db LICK -if !_CRYSTAL - db CHARM -endc db -1 ; end
Note that since Snorlax will now lay Munchlax eggs, it doesn't need Egg moves of its own, and its set of Egg moves can just be reused for Munchlax. Like the level-up moves, this data is unordered, since the
EggMovePointers table is used to access particular sets.
6. Define its cry
PokemonCries:: ; entries correspond to constants/pokemon_constants.asm mon_cry CRY_BULBASAUR, $080, $081 ; BULBASAUR ... mon_cry CRY_ENTEI, $14a, $111 ; CELEBI - mon_cry CRY_NIDORAN_M, 0, 0 ; 252 + mon_cry CRY_GRIMER, $065, $080 ; MUNCHLAX mon_cry CRY_NIDORAN_M, 0, 0 ; 253 mon_cry CRY_NIDORAN_M, 0, 0 ; 254 mon_cry CRY_NIDORAN_M, 0, 0 ; 255
The three values passed to
mon_cry are a cry index, a pitch, and a length. Defining your own cries is similar to writing original music, and well beyond the scope of this tutorial. So just pick a cry from constants/cry_constants.asm and tweak the pitch and length until it sounds okay. I simply copied Snorlax's cry for Munchlax, with a slightly higher pitch and shorter length.
7. Define its icon
MonMenuIcons: db ICON_BULBASAUR ; BULBASAUR ... db ICON_HUMANSHAPE ; CELEBI + db ICON_SNORLAX ; MUNCHLAX
Valid icons are in constants/icon_constants.asm. They're used in the party menu and Day-Care.
8. Define its Pokédex entry
+ db "BIG EATER@" ; species name + dw 200, 2315 ; height, weight + + db "In its desperation" + next "to gulp down food," + next "it forgets about" + + page "the food it has" + next "hidden under its" + next "fur.@"
- The species name can be up to 10 characters (technically 11 will still fit in the Pokédex window). Be sure to end it with a "@".
- The height and weight values are in imperial units. 200 = 2 feet 0 inches; 2315 = 231.5 pounds.
- The entry text is in two pages; the first starts with
db, the second with
page. Each page can fit three lines with 18 characters each. Here it's visual size that matters—
"#MON"counts as 7 characters because it prints as "POKéMON". Again, be sure to end it with a "@".
PokedexDataPointerTable: ; entries correspond to constants/pokemon_constants.asm dw BulbasaurPokedexEntry ... dw CelebiPokedexEntry + dw MunchlaxPokedexEntry
Then edit data/pokemon/dex_entries.asm:
SECTION "Pokedex Entries 193-251", ROMX PokedexEntries4:: YanmaPokedexEntry:: INCLUDE "data/pokemon/dex_entries/yanma.asm" ... CelebiPokedexEntry:: INCLUDE "data/pokemon/dex_entries/celebi.asm" +MunchlaxPokedexEntry:: INCLUDE "data/pokemon/dex_entries/munchlax.asm"
Each of the four sections in dex_entries.asm holds 64 Pokédex entries. Each section is in a different ROM bank, decided by which range the Pokémon's species ID is in: 1–64, 65–128, 129–192, or 193–256. The order of entries within each section doesn't actually matter, since they're accessed directly via
PokedexDataPointerTable, but avoid confusion and just keep them in numerical order.
Now the Pokédex entry exists, and will be listed correctly in "Old Pokédex Mode" (the Gen 2 equivalent of national order). But we need to define the new Pokémon's place in "New Pokédex Mode (regional order) and "A to Z Mode" (alphabetical order).
NewPokedexOrder: db CHIKORITA ... db AERODACTYL + db MUNCHLAX db SNORLAX db BULBASAUR ... db CELEBI
Then edit data/pokemon/dex_order_alpha.asm:
AlphabeticalPokedexOrder: db ABRA ... db MUK + db MUNCHLAX db MURKROW ... db ZUBAT
That's all for the Pokédex.
9. Design its footprint
Then edit gfx/footprints.asm:
; Footprints are 2x2 tiles each, but are stored as a 16x64-tile image ; (32 rows of 8 footprints per row). ; That means there's a row of the top two tiles for eight footprints, ; then a row of the bottom two tiles for those eight footprints. ; These macros help extract the first and the last two tiles, respectively. footprint_top EQUS "0, 2 * LEN_1BPP_TILE" footprint_bottom EQUS "2 * LEN_1BPP_TILE, 2 * LEN_1BPP_TILE" ; Entries correspond to Pokémon species, two apiece, 8 tops then 8 bottoms ... ; 249-256 top halves INCBIN "gfx/footprints/lugia.1bpp", footprint_top INCBIN "gfx/footprints/ho_oh.1bpp", footprint_top INCBIN "gfx/footprints/celebi.1bpp", footprint_top -INCBIN "gfx/footprints/252.1bpp", footprint_top +INCBIN "gfx/footprints/munchlax.1bpp", footprint_top INCBIN "gfx/footprints/253.1bpp", footprint_top INCBIN "gfx/footprints/254.1bpp", footprint_top INCBIN "gfx/footprints/255.1bpp", footprint_top INCBIN "gfx/footprints/256.1bpp", footprint_top ; 249-256 bottom halves INCBIN "gfx/footprints/lugia.1bpp", footprint_bottom INCBIN "gfx/footprints/ho_oh.1bpp", footprint_bottom INCBIN "gfx/footprints/celebi.1bpp", footprint_bottom -INCBIN "gfx/footprints/252.1bpp", footprint_bottom +INCBIN "gfx/footprints/munchlax.1bpp", footprint_bottom INCBIN "gfx/footprints/253.1bpp", footprint_bottom INCBIN "gfx/footprints/254.1bpp", footprint_bottom INCBIN "gfx/footprints/255.1bpp", footprint_bottom INCBIN "gfx/footprints/256.1bpp", footprint_bottom
Notice how the footprints are broken into top and bottom halves; you may want to correct this design flaw. (It won't have a visible consequence on the game, but it makes for cleaner code and data.)
make later will automatically create munchlax.1bpp from munchlax.png. Since it's a 1bpp file (one bit per pixel) you can only use black and white in the image.)
10. Design its sprites and animation
This is a bit complicated. We need a front sprite with an animation sequence; a back sprite; and normal and shiny color palettes for both.
front.png is a vertical strip of unique animation frames. Frames are all the same size; valid sizes are 40x40, 48x48, or 56x56. Here we have five frames, each 48x48 pixels. back.png is always 48x48. Both sprites have to use the same four colors: white, black, and the same two arbitrary hues.
Next create gfx/pokemon/munchlax/shiny.pal:
+ RGB 22, 22, 12 + RGB 07, 15, 25
These two colors will be used for shiny Munchlax, along with the standard black and white. The lighter color should come first.
Now create gfx/pokemon/munchlax/anim.asm:
+ frame 0, 08 + frame 1, 08 + frame 0, 08 + frame 2, 24 + frame 3, 08 + frame 4, 08 + frame 3, 08 + frame 3, 08 + frame 0, 16 + endanim
And finally gfx/pokemon/munchlax/anim_idle.asm:
+ frame 1, 08 + frame 0, 08 + frame 1, 08 + endanim
anim.asm defines the main sprite animation sequence; anim_idle.asm defines an extra one that gets played in some contexts (notably not when a Pokémon is encountered in battle). A full description of the animation script commands is at docs/pic_animations.md.
This Munchlax animation was designed by SCMidna. But you're more likely to have a single static front sprite than a whole animated sequence of frames. In that case, you can save the one sprite as front.png (so it will be a single square frame, not a vertical strip of them), and just put
endanim as the full contents of anim.asm and anim_idle.asm.
make the ROM, a number of sprite-related files will be automatically generated for you:
- front.gbcpal: Like shiny.pal, but for the normal colors; derived from front.png.
- front.dimensions: The size of the still sprite from front.png.
- front.animated.2bpp.lz: The compressed tiles needed to animate the sprite. Animation frames tend to have lots of duplicate tiles, since only parts of a Pokémon move at a time, so each unique tile only exists once.
- bitmask.asm: A sequence of masks that define which spots in each frame are changed from the still sprite.
- frames.asm: A sequence of lists that declare the tile IDs with which to fill in the changed spots in each frame.
There are two main reasons to pay attention to these auto-generated files. One, you want to make sure that front.gbcpal got its colors in the right order, and have shiny.pal match it. Two, if your animation appears corrupt, you want to make sure that frames.asm isn't using too high tile IDs. A 40x40 sprite can use IDs $00 to $31; a 48x48 sprite can use up to $47; a 56x56 sprite can use up to $61. If you see IDs above those limits, edit your front.png frames so they use fewer unique tiles.
(Older versions of pokecrystal generated normal.pal and normal.gbcpal files instead of front.gbcpal, but this was redundant work and could mislead users into editing normal.pal directly, so as of September 2018 they were removed.)
Anyway, all that's left is to
INCLUDE and point to to the new data!
11. Include and point to the sprite and animation data
PokemonPicPointers:: ; entries correspond to Pokémon species, two apiece dba_pic BulbasaurFrontpic dba_pic BulbasaurBackpic ... dba_pic CelebiFrontpic dba_pic CelebiBackpic - dbw -1, -1 ; unused - dbw -1, -1 ; unused + dba_pic MunchlaxFrontpic + dba_pic MunchlaxBackpic dba_pic EggPic dbw -1, -1 ; unused
We have to use
dba_pic here instead of a standard
dba—declaring the bank and address of
MunchlaxBackpic—because of another design flaw. I strongly recommend removing the whole
FixPicBank routine from engine/gfx/load_pics.asm, including all four calls to it in that file, and just using
dba here; then you'll be able to
INCBIN sprites in arbitrary banks.
SECTION "Pics 19", ROMX -; Seems to be an accidental copy of the previous bank - -INCBIN "gfx/pokemon/spinarak/back.2bpp.lz" -... -INCBIN "gfx/pokemon/unown_r/back.2bpp.lz" +MunchlaxFrontpic: INCBIN "gfx/pokemon/munchlax/front.animated.2bpp.lz" +MunchlaxBackpic: INCBIN "gfx/pokemon/munchlax/back.2bpp.lz"
(If you don't fix the
dba_pic design flaw, you'll have to put your sprites in the "Pics N" sections, which are compatible with
dba_pic. "Pics 19" isn't used for anything useful—all its contents are unused duplicates of "Pics 18"—and it has a whole bank to itself, so it's the easiest place to start adding new sprites. (The other sections, includng "Pics 20" through "Pics 24", have limited remaining space since they already contain some sprites and/or share their banks with other sections.) But if you have a lot of new sprites to add, you risk overflowing the banks, and it's hard to fit sprites within fixed bank limits. By using just
dba, you can create new sections with a few sprites each, that will automatically be placed wherever they can fit in the ROM.)
Anyway, edit data/pokemon/palettes.asm:
PokemonPalettes: ; entries correspond to Pokémon species, two apiece ; Each front.gbcpal is generated from the corresponding .png, and ; only the middle two colors are included, not black or white. ; Shiny palettes are defined directly, not generated. ; 000 RGB 30, 22, 17 RGB 16, 14, 19 ; 000 shiny RGB 30, 22, 17 RGB 16, 14, 19 INCBIN "gfx/pokemon/bulbasaur/front.gbcpal", middle_colors INCLUDE "gfx/pokemon/bulbasaur/shiny.pal" ... INCBIN "gfx/pokemon/celebi/front.gbcpal", middle_colors INCLUDE "gfx/pokemon/celebi/shiny.pal" -; 252 - RGB 30, 26, 11 - RGB 23, 16, 00 -; 252 shiny - RGB 30, 26, 11 - RGB 23, 16, 00 +INCBIN "gfx/pokemon/munchlax/front.gbcpal", middle_colors +INCLUDE "gfx/pokemon/munchlax/shiny.pal" INCBIN "gfx/pokemon/egg/front.gbcpal", middle_colors INCLUDE "gfx/pokemon/egg/shiny.pal" ; 254 RGB 30, 26, 11 RGB 23, 16, 00 ; 254 shiny RGB 30, 26, 11 RGB 23, 16, 00 ; 255 RGB 23, 23, 23 RGB 17, 17, 17 ; 255 shiny RGB 23, 23, 23 RGB 17, 17, 17
(Older versions of pokecrystal would
INCLUDE "normal.pal" instead of
INCBIN "front.gbcpal", as discussed earlier.)
AnimationPointers: dw BulbasaurAnimation ... dw CelebiAnimation + dw MunchlaxAnimation
PicAnimations: BulbasaurAnimation: INCLUDE "gfx/pokemon/bulbasaur/anim.asm" ... CelebiAnimation: INCLUDE "gfx/pokemon/celebi/anim.asm" +MunchlaxAnimation: INCLUDE "gfx/pokemon/munchlax/anim.asm" EggAnimation: INCLUDE "gfx/pokemon/egg/anim.asm"
AnimationIdlePointers: dw BulbasaurAnimationIdle ... dw CelebiAnimationIdle + dw MunchlaxAnimationIdle
BulbasaurAnimationIdle: INCLUDE "gfx/pokemon/bulbasaur/anim_idle.asm" ... CelebiAnimationIdle: INCLUDE "gfx/pokemon/celebi/anim_idle.asm" +MunchlaxAnimationIdle: INCLUDE "gfx/pokemon/munchlax/anim_idle.asm" EggAnimationIdle: INCLUDE "gfx/pokemon/egg/anim_idle.asm"
BitmasksPointers: dw BulbasaurBitmasks ... dw CelebiBitmasks + dw MunchlaxBitmasks
BulbasaurBitmasks: INCLUDE "gfx/pokemon/bulbasaur/bitmask.asm" ... CelebiBitmasks: INCLUDE "gfx/pokemon/celebi/bitmask.asm" +MunchlaxBitmasks: INCLUDE "gfx/pokemon/munchlax/bitmask.asm" EggBitmasks: INCLUDE "gfx/pokemon/egg/bitmask.asm"
FramesPointers: dw BulbasaurFrames ... dw CelebiFrames + dw MunchlaxFrames
Finally, edit gfx/pokemon/johto_frames.asm:
JohtoFrames: ChikoritaFrames: INCLUDE "gfx/pokemon/chikorita/frames.asm" ... CelebiFrames: INCLUDE "gfx/pokemon/celebi/frames.asm" +MunchlaxFrames: INCLUDE "gfx/pokemon/munchlax/frames.asm" EggFrames: INCLUDE "gfx/pokemon/egg/frames.asm"
Note that we edited johto_frames.asm, not kanto_frames.asm, because
MUNCHLAX comes after
JOHTO_POKEMON in constants/pokemon_constants.asm.
That's it—we're done! Munchlax works just like every other Pokémon.
12. Adding up to 253 Pokémon
We just added Pokémon #252; adding #253 is basically the same. However, instead of just replacing
MON_FE the way we replaced
MON_FC, I would recommend swapping
EGG. That way
MON_FE is $FD and
EGG is $FE.
This has multiple benefits:
- Pokémon IDs will be contiguous, from #1 to #253. No #254 with a missing #253 where Egg exists.
- Many data tables don't have an entry for
EGGsince it would be superfluous. But if there were a Pokémon #254, they would need filler entries for #253 in order to reach entry #254.
EGGdoes not count as a Pokémon, so if it came before a valid Pokémon ID, then
NUM_POKEMONwould have to be adjusted to compensate, and certain other checks in the code would no longer be able to assume that any ID below some number N is a valid one.
It's easy to do; just make sure that the various tables have their entries in the right order: Bulbasaur, Ivysaur, Venusaur, …, Celebi, #252, #253, Egg.
Unfortunately, you can't have more than 253 Pokémon. IDs are one byte each, so they have 256 possible values. Of those values, $00 indicates a lack of a Pokémon; $FF (−1) is an end-of-list marker; and $FD is
EGG (though you can change this to $FE, as discussed above). If you value having a 254th Pokémon more than allowing breeding, you could replace
EGG, but you would also have to carefully remove a lot of code that treats