In Generations I and II, there were two "Rat Pokémon" (Rattata and Raticate) and four "Mouse Pokémon" (Pikachu, Raichu, Sandshrew, and Sandslash) even though they shared the same Japanese category: 「ねずみポケモン」. From Generation III onwards, they are all known as "Mouse Pokémon".
If "Mouse Pokémon" and "Rat Pokémon" are counted as the same category (which has always been the case in Japanese), then this was the most abundant category in Generation I games, shared by 6 Pokémon. If those two categories are counted separately, then "Dragon Pokémon" was the most abundant category instead in this generation, shared by 5 Pokémon.
If "Mouse Pokémon" and "Rat Pokémon" are counted as the same category, then this was one of the most abundant categories in Generation II, shared by 6 Pokémon, while "Dragon Pokémon" was shared by 6 Pokémon as well. If "Mouse Pokémon" and "Rat Pokémon" are counted as separate categories, then "Dragon Pokémon" was the single most abundant category.
From Generation III to VIII, "Dragon Pokémon" was the most abundant category. It was shared by 7 Pokémon in Generations III–V, and 8 Pokémon in Generations VI–VIII.
In Generation IX, "Paradox Pokémon" became the most abundant category, with it being shared by 22 Pokémon overall.
