Proto Piranha

Gate Keepers are Piranha Plants covered in Goop created by Shadow Mario; they have only appeared in Super Mario Sunshine. They appear out of Goop Generators (hence and come in different colors. They periodically release Swoopin' Stus. To defeat them Mario had to shoot water in their mouth. During the first two encounters, Mario can defeat the Gate Keepers by squirting water in their mouth three times. However, during the last two encounters, Mario must squirt water into their mouth six times to defeat them.

In Mario Power Tennis, Petey Piranha's Defensive Power Shot involves him creating a Gate Keeper to hit an out of reach tennis ball for him.

Trivia

 * Although the generators are made of goop, Mario cannot wash the generators away like normal goop without defeating the Piranha Plant.