From the Super Mario Wiki
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The Yoofoe resembles a flying saucer UFO and a top hat. It has a purple Ground Pound symbol on its head followed by an inward facing black ring along the midsection of the enemy with a menacing red eye in the front of that black ring. The bottom section consists of a silver-colored dome-like structure. This enemy makes three appearances in the game: one in the Wooded Kingdom, another in Bowser's Kingdom and the last in the Darker Side. Upon defeat, a short cutscene plays with the Yoofoe spinning out of control and exploding. Mario is then rewarded one Power Moon, with the exception being the Darker Side in which a Life-Up Heart is rewarded instead. The Yoofoe is an alien invader, as suggested by the titles of the Power Moons received from it ("Invader in the Sky Garden" and "Invader in Bowser's Castle").
Initially, upon noticing Mario, the Yoofoe makes a piston noise and then shoots out five Goombas from its bottom. After this, it emits a red circular laser followed by two short razor bars. It then moves about the stage while rotating these bars. As it moves, it shoots out one small Spiked Ball followed by one Goomba. It repeats this pattern until Mario jumps on it from above. After getting hit once, it knocks Mario off its head and makes all the previously spawned Goombas disappear. It then expels a much larger red circular laser followed by four long razor bars instead of two short ones. It continues its previous pattern at this point, though every time it releases a Goomba, it spins its razor bars rapidly, thus Mario can only jump on the Yoofoe when it is not spinning.