The Mecha Hand is a large mechanical hand appearing in New Super Mario Bros. U and New Super Luigi U, and modeled after Bowser's own hand. It is attached to Bowser's airship, and it is most likely operated by Bowser Jr.
It is present during the intro, where it tosses Mario, Luigi, Yellow Toad, and Blue Toad into the Acorn Tree, The Mighty Cannonship (All Aboard! in New Super Luigi U), where it attempts to knock the players out of the airship, and Boarding the Airship (Bowser Jr. Showdown in New Super Luigi U) where it acts similarly to the Pillars in Super Mario World, and the Incoming Chomps from Super Mario World 2: Yoshi's Island. Ultimately, the hand destroys the airship when it attempts to crush the players while they are on board.
The LEGO Super Mario "Bowser's Airship" expansion set contains a Mecha Hand mounted on one of the ship's flagpoles.