Giga Cat Mario is a form of Mario that first appears in Super Mario 3D World + Bowser's Fury, albeit exclusively in the Bowser's Fury campaign. It is a larger, more powerful form of Cat Mario and is only accessible after collecting enough Cat Shines and unlocking the Giga Bell that is located in the middle of Lake Lapcat.
Befitting its status as a variation, Giga Cat Mario very much resembles Mario's standard Cat form, albeit much larger and presumably more powerful. His fur takes on a more radiant golden tint, with a mane and a tuff at the end of his tail, resembling those of a lion.