Egg Groups
Each Pokémon belongs to one or two egg groups (following Stadium 2's names). It can breed with other Pokémon from the groups it belongs too. Pokémon with unknown gender (Porygon foe example) can only breed with Ditto. However, Pokémon in the "Unbreedable" group are unable to produce eggs, neither with other Pokémon from the same group nor with Ditto. Ditto cannot breed with Ditto. Also have in mind that some Pokémon may not appear in some versions. Hint: In order to find in which other group a Pokémon belongs to, do Ctrl+F and search for the Pokémon you want.
Unbreedable Group
Articuno, Azurill, Celebi, Cleffa, Deoxys, Elekid, Entei, Groudon, Ho-oh, Igglybuff, Jirachi, Kyogre, Latias, Latios, Lugia, Magby, Mew, Mewtwo, Moltres, Nidoqueen, Nidorina, Pichu, Raikou, Rayquaza, Regice, Regirock, Registeel, Smoochum, Suicune, Togepi, Tyrogue, Unown, Wynaut, Zapdos
Bug Group
Ariados, Beautifly, Beedrill, Butterfree, Cascoon, Caterpie, Dustox, Flygon, Forretress, Gligar, Heracross, Illumise, Kakuna, Ledian, Ledyba, Masquerain, Metapod, Nincada, Ninjask, Paras, Parasect, Pineco, Pinsir, Scizor, Scyther, Shuckle, Silcoon, Spinarak, Surskit, Trapinch, Venomoth, Venonat, Vibrava, Volbeat, Weedle, Wurmple, Yanma
Dragon Group
Altaria, Arbok, Bagon, Charizard, Charmander, Charmeleon, Dragonair, Dragonite, Dratini, Ekans, Feebas, Grovyle, Gyarados, Horsea, Kingdra, Magikarp, Milotic, Salamence, Sceptile, Seadra, Seviper, Shelgon, Swablu, Treecko
Fairy Group
Azumarill, Blissey, Breloom, Castform, Chansey, Clefable, Clefairy, Delcatty, Glalie, Granbull, Hoppip, Jigglypuff, Jumpluff, Marill, Mawile, Minun, Pikachu, Plusle, Raichu, Roselia, Shroomish, Skiploom, Skitty, Snorunt, Snubbull, Togetic, Wigglytuff
Flying group
Aerodactyl, Altaria, Crobat, Dodrio, Doduo, Farfetch'd, Fearow, Golbat, Hoothoot, Murkrow, Natu, Noctowl, Pelipper, Pidgeot, Pidgeotto, Pidgey, Skarmory, Spearow, Swablu, Swellow, Taillow, Togetic, Wingull, Xatu, Zubat
Ground Group
Absol, Aipom, Arbok, Arcanine, Blaziken, Camerupt, Combusken, Cyndaquil, Delcatty, Delibird, Dewgong, Diglett, Donphan, Dugtrio, Dunsparce, Eevee, Ekans, Electrike, Espeon, Farfetch'd, Flareon, Furret, Girafarig, Golduck, Granbull, Growlithe, Grumpig, Houndoom, Houndour, Jolteon, Kecleon, Linoone, Manectric, Mankey, Mawile, Meowth, Mightyena, Miltank, Ninetales, Numel, Nuzleaf, Persian, Phanpy, Pikachu, Piloswine, Ponyta, Poochyena, Primeape, Psyduck, Quagsire, Quilava, Raichu, Rapidash, Raticate, Rattata, Sandshrew, Sandslash, Sealeo, Seedot, Seel, Sentret, Seviper, Shiftry, Skitty, Slaking, Slakoth, Smeargle, Sneasel, Snubbull, Spheal, Spinda, Spoink, Stantler, Swinub, Tauros, Teddiursa, Torchic, Torkoal, Typhlosion, Umbreon, Ursaring, Vaporeon, Vigoroth, Vulpix, Wailmer, Wailord, Walrein, Wooper, Zangoose, Zigzagoon
Humanshape Group
Abra, Alakazam, Cacnea, Cacturne, Drowzee, Electabuzz, Hariyama, Hitmonchan, Hitmonlee, Hitmontop, Hypno, Illumise, Jynx, Kadabra, Machamp, Machoke, Machop, Magmar, Makuhita, Medicham, Meditite, Mr.Mime, Sableye, Spinda, Volbeat
Indeterminate
Banette, Castform, Chimecho, Dusclops, Duskull, Gardevoir, Gastly, Gengar, Grimer, Gulpin, Haunter, Kirlia, Koffing, Magcargo, Misdreavus, Muk, Ralts, Shuppet, Slugma, Swalot, Weezing, Wobbuffet
Mineral Group
Baltoy, Beldum, Claydol, Electrode, Geodude, Glalie, Golem, Graveler, Lunatone, Magnemite, Magneton, Metagross, Metang, Nosepass, Onix, Porygon, Porygon2, Shedinja, Snorunt, Solrock, Steelix, Sudowoodo, Voltorb
Monster Group
Aggron, Ampharos, Aron, Bayleef, Blastoise, Bulbasaur, Charizard, Charmander, Charmeleon, Chikorita, Croconaw, Cubone, Exploud, Feraligatr, Flaaffy, Grovyle, Ivysaur, Kangaskhan, Lairon, Lapras, Larvitar, Lickitung, Loudred, Mareep, Marowak, Marshtomp, Meganium, Mudkip, Nidoking, Nidoran ♀, Nidoran ♂, Nidorino, Pupitar, Rhydon, Rhyhorn, Sceptile, Slowbro, Slowking, Slowpoke, Snorlax, Squirtle, Swampert, Totodile, Treecko, Tropius, Tyranitar, Venusaur, Wartortle, Whismur
Plant Group
Bayleef, Bellossom, Bellsprout, Breloom, Bulbasaur, Cacnea, Cacturne, Chikorita, Exeggcute, Exeggutor, Gloom, Hoppip, Ivysaur, Jumpluff, Lombre, Lotad, Ludicolo, Meganium, Nuzleaf, Oddish, Paras, Parasect, Roselia, Seedot, Shiftry, Shroomish, Skiploom, Sunflora, Sunkern, Tangela, Tropius, Venusaur, Victreebel, Vileplume, Weepinbell
Water 1 Group
Azumarill, Blastoise, Clamperl, Corphish, Corsola, Crawdaunt, Croconaw, Delibird, Dewgong, Dragonair, Dragonite, Dratini, Feebas, Feraligatr, Golduck, Gorebyss, Horsea, Huntail, Kabuto, Kabutops, Kingdra, Lapras, Lombre, Lotad, Ludicolo, Mantine, Marill, Marshtomp, Masquerain, Milotic, Mudkip, Octillery, Omanyte, Omastar, Pelipper, Politoed, Poliwag, Poliwhirl, Poliwrath, Psyduck, Quagsire, Relicanth, Remoraid, Seadra, Sealeo, Seel, Slowbro, Slowking, Slowpoke, Spheal, Squirtle, Surskit, Swampert, Totodile, Walrein, Wartortle, Wingull, Wooper
Water 2 Group
Barboach, Carvanha, Chinchou, Goldeen, Gyarados, Lanturn, Luvdisc, Magikarp, Octillery, Qwilfish, Relicanth, Remoraid, Seaking, Sharpedo, Wailmer, Wailord, Whiscash
Water 3 Group
Anorith, Armaldo, Cloyster, Corphish, Corsola, Cradily, Crawdaunt, Kabuto, Kabutops, Kingler, Krabby, Lileep, Omanyte, Omastar, Shellder, Starmie, Staryu, Tentacool, Tentacruel
Ditto Group
Ditto