Field (egg group)
This is by far the largest egg group, previously known as
Ground. As well as having many Ground type Pokémon, the Field group contains lots of land-based mammals and has the most diverse range of types. This makes for easy breeding of multiple moves. Oddly (perhaps disturbingly), this group contains Wailord, one of the largest Pokémon in existence, and some of the smallest like Skitty and Diglett.