Chimeras are a fearsome kind of mythological monster that lives in Equestria. It made its debut in the season 4 episode Somepony to Watch Over Me. They are three headed creatures that are part tiger, part goat and part snake. It is based on its Greek myth counterpart. Despite its bestial appereance, it is sentient and can talk like the ponies.
Apple Bloom encounters the monster in the Flame Geyser Swamp on her way to deliver apple pies to a faraway town for Applejack. The chimera attacks Apple Bloom with intent of eating her and the pies, but Applejack saves her and tames the monster with a snake-charming flute, a lion tamer's chair, and a hunk of ricotta cheese. The three heads address each other as sisters, and suggest a history of bickering with each other, claiming they can never agree on what to eat, and fighting over who should be in charge.