Nabbit

Nabbit is an enemy introduced in New Super Mario Bros. U. He is a thief who steals items from Toad Houses and runs away with it. If the players finds him in a level, they can grab him and gain a P-Acorn.

The mask he wears resembles the mask Bowser Jr. wears, so he presumably has an affiliation with the Koopa Troop.

Trivia

 * "Nabbit" is a play on the words "nab it" and rabbit.