Rule Book appears in 10 version groups since Generation IV, an Unused item in the Key Items pocket
PokéAPI item 407 of 2,223, Unused category, Key Items pocket
Effect, in PokéAPI's words
Rule Book: “List of battle types and their rules.”
Unused.
Games
Rule Book is listed in the text of 10 version groups, first in Generation IV
Game index by generation
IIIIIIIVVVIVIIVIIIIX
Named in
Diamond and PearlPlatinumHeartGold and SoulSilverBlack and WhiteBlack 2 and White 2X and YSun and MoonUltra Sun and Ultra MoonLet's Go Pikachu and Let's Go EeveeSword and Shield