From the Super Mario Wiki
Not to be confused with Cheep Chump.
Cheep Chomps are Cheep Cheeps that are bigger than usual and are first found in underwater levels in New Super Mario Bros.. They closely resemble a Boss Bass. These Cheep Cheeps are purple with a green back-fin and have enormous mouths.
Super Mario series
New Super Mario Bros.
In New Super Mario Bros., if Mario or Luigi swim too close to the Cheep Chomp, it opens its mouth and tries to eat the adventurer. The giant fish often follows the character around the screen while attempting to devour them. Success on their part causes the player to lose a life, regardless of the player's condition. They can be defeated, like all other fish, with a Fireball or being smashed by Mega Mario/Luigi. Only four appear in the entire game, all of them appearing in the same level: World 3-1.
New Super Mario Bros. Wii
In New Super Mario Bros. Wii, only two Cheep Chomps appear: Once in a bonus area in 4-4, and again in a bonus area of 9-2. A Fireball or Starman takes the big fish down, but it is invincible to ice balls from Ice Mario. Two changes are made from New Super Mario Bros.: it is slightly bigger, and defeating it releases three 1-Up Mushrooms.
New Super Mario Bros. 2
Cheep Chomps once again appear in New Super Mario Bros. 2. One makes it first appearance early in World 1-5. When defeated, it releases 3 coins. They reappear as common enemies in World 4-5. Another appears in course 1 of the Impossible Pack, near two whirlpools.
New Super Mario Bros. U
The Cheep Chomps reappear in New Super Mario Bros. U and act as in the predecessors. This enemy is prominently featured in the Superstar Road level Swim for Your Life!, where it must be used to eat Urchins and other enemies to complete the level. This time, it takes three hits from a fireball to be defeated. However, like a Porcupuffer, it returns in a short while, though it returns almost immediately after it is defeated.
New Super Luigi U
In New Super Luigi U, Cheep Chomps appear in Cheep Chomp Chase in Acorn Plains and Star Coin Deep Dive in Superstar Road. Cheep Chomps, Magmaarghs, and Magmaws are the only enemies who can defeat Nabbit.
Paper Mario: Sticker Star
A giant Cheep Chomp appears in Paper Mario: Sticker Star as an obstacle. It can be seen on the surface of the water in Long Fall Falls, pursuing Mario (who is riding a raft down the river). The Cheep Chomp appears to be made of cardboard, featuring a propeller-like tail. The Cheep Chomp can destroy parts of the raft Mario is riding on by ramming into it, and being eaten results in an instant Game Over. When both reach a waterfall, Mario and his raft continue to fall, while the Cheep Chomp's "propeller" ends up propelling it upward, into space.
Mario Party: Island Tour
Cheep Chomps appear in Mario Party: Island Tour in the minigame Cheep Diamonds. They swallow an amount of diamonds and then circle around in the water; the players are trying to pick the Cheep Chomp that swallowed the most diamonds.
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