Complex sentence: Some enemies will have small green UFOs circling above them, they drop a small UFO after you destroy them, some stage mid-bosses will drop 2 small UFOs after you defeat their final attack.
Split into simpler sentences: Some enemies will have small green UFOs circling above them. They drop a small UFO after you destroy them, and some stage mid-bosses will drop 2 small UFOs after you defeat their final attack.