Cat Mario: Super Bell power-up is OP
Cat Mario is one of Mario's new transformations and it made its first appearance in Super Mario 3D World on the Wii U. Mario has had a long history of power-ups and costumes, Fire Mario, Raccoon Mario, Tanooki Mario, Cape Mario, Frog Mario, Hammer Bro Mario, Ice Mario, Squirrel Mario... the list goes on.
Mario can turn into Cat Mario by collecting the Super Bell power-up. Usually, this would be in a question block when he is in "big" form, the Super Bell can also sometimes be scattered around worlds and can be picked up.
Cat Mario has a great deal of abilities, and arguably this is one of the most overpowered (OP) power-ups in the Mario series. When in this form, Mario can climb up walls and trees, swipe/claw enemies on the ground and even in the air.
The claw attack actually makes Super Mario 3D World significantly easier to play. In normal form, Mario is only capable of running and jumping, just like a traditional 2D platformer - there is no other way to attack. When you are Cat Mario you can just run and plow down most enemies that are along your path, making the adventure far more of a breeze.
This power-up actually has some similarities to Tanooki Mario from Super Mario Bros 3, Super Mario 3D Land and Super Mario 3D World. They are both full body animal suits effectively, and give Mario an additional attack - claw attack for Cat Mario and a tail whip attack for Tanooki Mario.
In Cat form, he can even climb up the flagpole at the end of the levels to nearly guarantee a gold flag! The ability to easily grab a gold flag can save a great deal of time to get full completion you need to reach the top of the flag in every stage.
In Super Mario Maker 2 for the Nintendo Switch, Cat Mario makes a return in the Super Mario 3D World game style, which is ironic considering this is a 2D sidescroller game. He has the same functions and abilities, making him just as OP as he was in Super Mario 3D World.