A Mecha Cheep is a mechanical version of Cheep-Cheep that first appears in New Super Mario Bros. U. They have metal fins and a wind-up key at the back similar to that of Mecha-Koopas.
A Mecha Cheep in New Super Mario Bros. U
In the game, Mecha Cheeps appear only in the level The Mighty Cannonship. They're impervious to Fireballs, but can be defeated with an Iceball or Star, or by leading a Targeting Ted into them.