Yoofoe

Overview
Yoofoes are round purple enemies that appear in Super Mario Odyssey. They appear to be robotic flying saucers, and only appear in specific kingdoms once the main quests for that kingdom have been completed. Once defeated, they will reward the player with a power moon.

Battle
Yoofoes have two phases. During the first phase, two long spikey bars extend from the sides and slowly orbit it. The yoofoe will then fly around the area, dropping goombas and spikey balls. (Only 8 goombas can be dropped at a time. After that, the yoofoe will only drop spike balls.) Mario must capture a goomba and build a stack high enough to allow him to stomp on the yoofoe while avoiding the spike bars. It will then enter its second phase. In its second phase, the yoofoe extends four longer spike bars instead of two, but the fight is otherwise unchanged. Stomping the yoofoe a second time will defeat it.

Locations
One yoofoe appears in the wooded kingdom above the arena Spewart was first fought in. The second one is in Bowser's kingdom above one of the two broodal fight arenas. Their battle mechanics are identical.

Trivia
The name "yoofoe" appears to be a combination of "UFO" (referencing their similarity to flying saucers), and "foe" (referencing the fact that they are enemies).