801 rule changes across 8 generations, Generation V the busiest with 471

One row per change: type chart cells, move power, accuracy, PP, effect chance and type, species types, and abilities, Generations II to IX.

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

Counts

Generation V alone holds 471 of the 801 rows

Every row names one subject, one field, the value before and the value after. Each generation opens its own page.

Gen	Type chart cells	Types added	Move stats	Move types	Species types	Abilities	All
II	4	2	22	4	2		34
III			5				5
IV			20			89	109
V			52	1		418	471
VI	2	1	78	3	22	23	129
VII			18			15	33
VIII			8			2	10
IX			1			9	10
All	6	3	204	8	24	556	801

by kind

212 rows

150 subjects, Generations II, III, IV, V, VI, VII, VIII and IX

9 rows

8 subjects, Generations II and VI

24 rows

24 subjects, Generations II and VI

556 rows

454 subjects, Generations IV, V, VI, VII, VIII and IX

Type chart

Gen	Type	Field	Before	After
II	Bug	against Poison	×2	×½
II	Dark	new type	None	Dark
II	Ghost	against Psychic	×0	×2
II	Ice	against Fire	×1	×½
II	Poison	against Bug	×2	×1
II	Steel	new type	None	Steel
VI	Dark	against Steel	×½	×1
VI	Fairy	new type	None	Fairy
VI	Ghost	against Steel	×½	×1

Largest power changes

Gen	Move	Field	Before	After
II	Explosion	power	170	250
VII	Solar Beam	power	120	200
VIII	Solar Beam	power	200	120
II	Self-Destruct	power	130	200
VII	Leech Life	power	20	80
VII	Sky Attack	power	140	200
VIII	Sky Attack	power	200	140
VI	Hidden Power	power	1	60
VI	Synchronoise	power	70	120
VI	Knock Off	power	20	65
II	Dig	power	100	60
V	Uproar	power	50	90

Species

Abilities

Gen	Species	Field	Before	After
VI	Chandelure	hidden ability	Shadow Tag	Infiltrator
VI	Lampent	hidden ability	Shadow Tag	Infiltrator
VI	Litwick	hidden ability	Shadow Tag	Infiltrator
VI	Scolipede	hidden ability	Quick Feet	Speed Boost
VI	Venipede	hidden ability	Quick Feet	Speed Boost
VI	Whirlipede	hidden ability	Quick Feet	Speed Boost
VI	Zapdos	hidden ability	Lightning Rod	Static
VII	Entei	hidden ability	Flash Fire	Inner Focus
VII	Gengar	ability slot 1	Levitate	Cursed Body
VII	Raikou	hidden ability	Volt Absorb	Inner Focus
VII	Suicune	hidden ability	Water Absorb	Inner Focus
IX	Basculegion	ability slot 1	Rattled	Swift Swim
IX	Empoleon	hidden ability	Defiant	Competitive
IX	Enamorus	ability slot 1	Healer	Cute Charm
IX	Kleavor	hidden ability	Steadfast	Sharpness
IX	Piplup	hidden ability	Defiant	Competitive
IX	Prinplup	hidden ability	Defiant	Competitive
IX	Shiftry	ability slot 2	Early Bird	Wind Rider