Cheep-Chomp

From the Super Mario Wiki

A Cheep-Chomp attacking.

Cheep-Chomps are enormous Cheep-Cheeps found in underwater levels in New Super Mario Bros.

These Cheep-Cheeps are purple with a green backfin and have enormous mouths. If Mario or Luigi swim too close to the Cheep-Chomp, it will open its mouth and try to eat the adventurer. The giant fish will often follow the character around the screen while attempting to devour him. Success on their part causes the player to lose a life. They can be defeated, like all other fish, with a Fireball or being smashed by Mega Mario/Luigi. They do not appear in small versions.

In this respect, the Cheep-Chomp is a lot like the Boss Bass from Super Mario Bros. 3.