Big Fishy is a gigantic robotic-fish that works for the Tabemon Monsters in the video-game "The Munchables".
Like many robots in fiction he is very aggressive and is programmed to attack any and all intruders, which just happens to be the Great Elder and the hero of the story.
Big Fishy fought via swimming and sucking in air much like a vacuum in an attempt to eat the hero (which, admitedly, was rather ironic since most of the story revolved around the hero trying to devour the aliens).
It could also turn into a razor-sharp ball and spin at the hero but was vulnerable whenever its stomach was exposed and thus was eventually devoured by the hero.