From the Super Mario Wiki, the Mario encyclopedia
A Proto Piranha, originally known as Gatekeeper, is a large species of Piranha Plant composed entirely of goop. They appear as enemies in Super Mario Sunshine, Mario Power Tennis, and Mario Golf: Advance Tour.
In Super Mario Sunshine, Gatekeepers appear out of Generators in several areas towards the beginning of the game. To get the Gatekeeper to come out of its base, Mario has to spray it with F.L.U.D.D. until it comes out. In order to defeat one, Mario must use F.L.U.D.D. to shoot water into its open mouth repeatedly. If Mario sprays one while its mouth is closed, it merely shrugs the attack off. Once defeated, Gatekeepers dissolve into goop, after which their base disappears; Mario cannot wash away a goop base like he can with normal goop. Aside from periodically spawning Swoopin' Stus, a Gatekeeper does nothing to attack, and will actually retreat back into its base if Mario does not defeat it in time. There are three different types of Gatekeepers in the game:
It is also worth noting that the brown one in Bianco Hills is the only one that can be fought multiple times, due to it being the only one in a replayable episode and the rest being fought in Delfino Plaza or Delfino Airstrip to unlock portals to other areas.
In Mario Golf: Toadstool Tour, Gatekeeper, renamed Proto Piranha, appears as a name on the leaderboard.
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