pokeemerald/include/constants/pokemon_config.h

#ifndef GUARD_CONSTANTS_POKEMON_CONFIG_H
#define GUARD_CONSTANTS_POKEMON_CONFIG_H

#ifndef GEN_3
#define GEN_3 0
#define GEN_4 1
#define GEN_5 2
#define GEN_6 3
#define GEN_7 4
#define GEN_8 5
#endif

#define P_UPDATED_TYPES         GEN_8 // Since Gen 6, several Pokémon were changed to be partially or fully Fairy type.
#define P_UPDATED_STATS         GEN_8 // Since Gen 6, Pokémon stats are updated with each passing generation.
#define P_UPDATED_ABILITIES     GEN_8 // Since Gen 6, certain Pokémon have their abilities changed.
#define P_UPDATED_EGG_GROUPS    GEN_8 // Since Gen 8, certain Pokémon have gained new egg groups.
#define P_SHEDINJA_BALL         GEN_8 // Since Gen 4, Shedinja requires a Poké Ball for its evolution. In Gen 3, Shedinja inherits Nincada's Ball.
#define P_LEGENDARY_PERFECT_IVS GEN_8 // Since Gen 6, Legendaries, Mythicals and Ultra Beasts found in the wild or given through gifts have at least 3 perfect IVs.
#define P_KADABRA_EVERSTONE     GEN_8 // Since Gen 4, Kadabra can evolve even when holding an Everstone.
#define P_NIDORAN_M_DITTO_BREED GEN_8 // Since Gen 5, when Nidoran♂ breeds with Ditto it can produce Nidoran♀ offspring. Before, it would only yield male offspring. This change also applies to Volbeat.

// Modifying the latest generation WILL change the saveblock due to Dex flags and will require a new save file.
// Forms are kept based on the base species, Eg: Meowth and Persian will keep all of their forms, but Perrserker will not be available if P_GEN_8_POKEMON is set to FALSE.
// If you're disabling a generation previous to others (eg: Gen 5 but not Gen 6, 7 and 8),
// remember to update NATIONAL_DEX enum in include/constants/pokedex.h to avoid players from softlocking in the non-existant entries.
#define P_GEN_4_POKEMON         TRUE  // Generation 4 Pokémon (DPPt, HGSS)
#define P_GEN_5_POKEMON         TRUE  // Generation 5 Pokémon (BW, B2W2)
#define P_GEN_6_POKEMON         TRUE  // Generation 6 Pokémon (XY, ORAS)
#define P_GEN_7_POKEMON         TRUE  // Generation 7 Pokémon (SM, USUM)
#define P_GEN_8_POKEMON         TRUE  // Generation 8 Pokémon (SwSh, BDSP, LA)

#define P_ENABLE_DEBUG          TRUE  // Enables a debug menu for pokemon sprites and icons, accessed by pressing SELECT in the summary screen.

#endif // GUARD_CONSTANTS_POKEMON_CONFIG_H