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. Her name comes from the fact that she resides in water. Exclusive to only this boss, there is an alternate way to beat her. If you stand on the very edge of the ledge she stands on, you can simply throw an egg at her "unmodified" form to kill her 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. She frequently uses hearts in her dialogue, and calls Yoshi "Babeh" so it is presumed she is female.