Nabbit is a recurring character in the Mario franchise. He made his first appearance in the New Super Mario Bros. U game in 2012 as an enemy, but will become a playable character thereafter and will continue to make appearances in several games.
He is a little brigand bunny who has a scarf which reminds the Bowser Jr.'s one, although no link has really been established between the two characters to this day.
He notably commits his theft from the Toad before burying the stolen objects in his bag and fleeing at full speed. That's when Mario and his friends can start a chase to help the mushroom creatures and get a reward from them if they've managed to catch up with the scoundrel.