Skipsqueak

Beach Mice are mouse-like enemies that appear in Super Mario 3D World and Super Mario 3D World + Bowser's Fury. Their name is a portmanteau of "Beach" and "Mouse".

Super Mario 3D World / Super Mario 3D World + Bowser's Fury
In Super Mario 3D World, Beach Mice constantly run on moving platforms going in the opposite direction, causing them to remain in one place. They also jump up periodically while shouting "chu!", and are usually found in groups of two or more. Beach Mice can be defeated by using any form of attack, including a jump attack. They appear in the levels Really Rolling Hills, The Bowser Express, Grumblump Inferno, Rainbow Run, and Night Falls on Really Rolling Hills.

There is a variation of this enemy known as Spiny Beach Mouse which appear in Cookie Cogworks, Rainbow Run, and Night Falls on Really Rolling Hills.

In the Bowser's Fury mode, new cat variations featuring cat ears and a tail appear, and are known as Cat Beach Mice. They act the same as normal Beach Mice. Cat Beach Mice appear exclusively on the Slipskate Slope island, found on rotating tunnels that appear there.

Super Mario Maker 2
Beach Mice and Spiny Beach Mice reappear as enemies that can be placed in Super Mario Maker 2 stages. Beach Mice jump whenever Mario jumps, and run in place to keep up with Conveyor Belts. If a Beach Mouse is pushed away from its starting point, such as by a Thwomp or Track Block, it will run back towards its starting point and even Triple Jump over obstacles to get there. If it cannot pass an obstacle, it will give up and look tired, and then resets its movement pattern from its new location. Beach Mice also appear in Story Mode, in the level Skipsqueak Towers.

Super Mario Maker 2

 * North American website bio: Beach Mice like to try and match Mario’s jumps. Sometimes you can use that to your advantage!