Guppy

"What, you again? You got to be kidding me! You want to run me out of this lake? You got to get through all eight rings!"

- Guppy

Guppy is a rival character in Super Mario Galaxy. He is an orca with a shark-like body shape who appears in Sea Slide Galaxy and Deep Dark Galaxy, where during one mission in each galaxy, he "takes over" a large body of water, and if Mario wishes to take it back, he has to swim through eight rings in a set amount of time. After Mario does that, Guppy rewards him with a Power Star.

Guppy appears in the moat of Peach's Castle in the Mushroom Kingdom at the end of the game, after the universe had been saved by the Lumas.

If Mario touches Guppy, Mario bounces back on the ground and lose a Shell if he is holding one, but he will not take damage.

Super Mario Galaxy trading card description
''Guppy's bark is definitely worse than his bite. This orca may look menacing, but he's really only aggressive to penguins and Toads. To Mario, Guppy is ultimately harmless, but he does present two challenges: he'll make Mario swim through eight rings in one body of water, and if Mario bumps into him, Guppy will bounce him to the floor. Look for Guppy in the Sea Slide Galaxy and the Deep Dark Galaxy.''

Trivia

 * The developers for Super Mario Galaxy initially envisioned Guppy as one of the friendly dolphins from Super Mario World. However, as his role was finalized as an intimidating bully with wild nature, they shifted his design to that of the new orca character seen in the final game.
 * There is an illustration of Guppy on his with an  hanging out of his mouth that has air bubbles trailing out the end, a potential allusion to a . There is no anchovy in Guppy's mouth in the final release.
 * In at least some international releases of Super Mario Galaxy, Guppy does not directly refer to himself as an orca and parts of his dialogue suggests he thinks of himself as a fish. In the German version of the game, Guppy explicitly refers to himself as a shark.
 * In Deep Dark Galaxy, Guppy will act as if he met Mario even if he has not been encountered in the Sea Slide Galaxy yet.
 * The PRIMA Official Game Guide erroneously states that Guppy is a shark.