Slowpoke Tail appears in 8 version groups since Generation II, an Unused item in the Key Items pocket
PokéAPI item 473 of 2,223, Unused category, Key Items pocket
Effect, in PokéAPI's words
Slowpoke Tail: “A tasty tail that sells for a high price.”
Does nothing.
Games
Slowpoke Tail is listed in the text of 8 version groups, first in Generation II
Game index by generation
IIIIIIIVVVIVIIVIIIIX
Named in
HeartGold 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