24 species changed type, 22 of them to take Fairy in Generation VI

The other 2 changes: Magnemite from Electric to Electric and Steel in Generation II and Magneton from Electric to Electric and Steel in Generation II.

Main-series rules that PokéAPI records as past values, plus the ordinary type chart by era; default forms only.

Every row

24 rows across 2 generations

Gen	Species	Field	Before	After
II	Magnemite	types	Electric	Electric and Steel
II	Magneton	types	Electric	Electric and Steel
VI	Azumarill	types	Water	Water and Fairy
VI	Azurill	types	Normal	Normal and Fairy
VI	Clefable	types	Normal	Fairy
VI	Clefairy	types	Normal	Fairy
VI	Cleffa	types	Normal	Fairy
VI	Cottonee	types	Grass	Grass and Fairy
VI	Gardevoir	types	Psychic	Psychic and Fairy
VI	Granbull	types	Normal	Fairy
VI	Igglybuff	types	Normal	Normal and Fairy
VI	Jigglypuff	types	Normal	Normal and Fairy
VI	Kirlia	types	Psychic	Psychic and Fairy
VI	Marill	types	Water	Water and Fairy
VI	Mawile	types	Steel	Steel and Fairy
VI	Mime Jr.	types	Psychic	Psychic and Fairy
VI	Mr. Mime	types	Psychic	Psychic and Fairy
VI	Ralts	types	Psychic	Psychic and Fairy
VI	Snubbull	types	Normal	Fairy
VI	Togekiss	types	Normal and Flying	Fairy and Flying
VI	Togepi	types	Normal	Fairy
VI	Togetic	types	Normal and Flying	Fairy and Flying
VI	Whimsicott	types	Grass	Grass and Fairy
VI	Wigglytuff	types	Normal	Normal and Fairy