From the Super Mario Wiki
Mario fighting off some Cheep Cheep Pufferfish
The Cheep Cheep Pufferfish is one of the bosses in Mario Pinball Land. It is found inside a shipwreck in Frosty Frontier. Its name comes from the fact that it is half Cheep Cheep and half pufferfish, having spikes on its body. When hit by Bob-ombs, it will inflate, leaving it vulnerable to Mario's pinball form. It will mainly swim around its lair calmly, but after enough time has passed, it will extend the spikes on its body and home in on Mario directly to knock him around the room. Every time it takes a hit, it will summon two smaller versions of itself to help it attack (or a single new one if one has already been defeated). These foes can be destroyed by flicking a single Bob-omb at them with the pinball flippers.