The Mad Moon (or more commonly known as the Angry Moon) is an enemy serving as the counterpart to Angry Sun which appears in both Newer Super Mario Bros. Wii and Newer Super Mario Bros. DS. It is a moon with an angry face and a variety of iceball-based attacks.
The Mad Moon is a grey moon with an extremely infuriated expression. It has red eyes with yellow irises.
The Mad Moon acts exactly like the Angry Sun, but instead of shooting fireballs; it shoots iceballs. The Mad Moon can attack by swooping down at the players, spitting out one or three iceballs at a time, or moving in a spiral pattern. It can be defeated by throwing a Koopa shell or frozen enemy at it, touching it with a Super Star active, or by touching the Checkpoint Flag or Flagpole.
The Mad Moon is a 2D sprite ripped straight from Newer Super Mario Bros. Wii. Therefore, it looks the exact same.
Since the Ice Flower and the Penguin Suit weren't in the original New Super Mario Bros., iceballs weren't a thing. So the Newer Team had to figure out a way to differentiate the Mad Moon from the Angry Sun. They did this by making the Mad Moon more aggressive, and they made it shoot more recolored fireballs than the Angry Sun. It can be defeated by the same means as Newer Super Mario Bros. Wii, but now we know it can be defeated by Red Rings.