Naval Piranha

 Naval Piranha is the boss of Level 3-8 in Super Mario World 2: Yoshi's Island, and later in the GBA remake. Its name comes from the fact that he resides in water. Exclusive to only this boss, there is an alternate way to beat him. If you stand on the very edge of the ledge he stands on, you can simply throw an egg at his "unmodified" form to kill him in one hit. Kamek will then come in, surprised, only to say "OH NO!!" and fly off again.

In Tetris Attack, Naval Pirahna is the tenth level and the boss of easy vs. mode.