Reo

A Rio, also spelled Reo in some games, is a relatively powerful enemy found mainly in Brinstar. They appear in Metroid and its remake, as well as Super Metroid. The Sentry Drones of Metroid Prime are designed similarly to them as well. Rios fly back and forth until they see Samus, at which point they execute a swooping dive attack with their tallons. They can take much more damage than most other early-game enemies in the first Metroid.