Mecha Cheep are uncommon enemies found in the Mario series. They are mechanized versions of Cheep Cheeps.
New Super Mario Bros. U/New Super Luigi U/New Super Mario Bros. U Deluxe
In all three versions of these games, Mecha Cheeps make their first appearance (in the original, Wii U version). They are found in The Mighty Airship, where they swim straightforward. Because of their larger size compared to their organic counterpart, they're harder to dodge. They also cannot be defeated by fireballs. However, they can be frozen and defeated if they are floated to the top of the ceiling while frozen.
Mario Kart 8/Mario Kart 8 Deluxe
In both versions of these games, Mecha Cheeps are seen swimming in the water section of Water Park. There is also a poster found in the same course that details there structure and different mechanisms.