Guppy

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Guppy is a character in Super Mario Galaxy for the Wii. He resembles a killer whale, though obviously with a more Mario theme to it. While he looks like an enemy, he is actually just considered a bully to the residents of the game's worlds, as he tends to take over the game's multiple seas. If Mario ever spots him in the game, then this usually means that he'll have to swim through eight specifically placed rings that the whale places around the area in subject (though note that it'll always be in water).