From the Super Mario Wiki
Huckit Crabs are a species of red crabs consisting of a shell, two yellow feet and only one claw that it uses to throw either sand balls or rocks. They also have an endless supply of projectiles. Their goal is to hit Mario and his company with their projectiles, which travel in a straight line when thrown.
Super Mario series
New Super Mario Bros. Wii
In New Super Mario Bros. Wii, Huckit Crabs appear only in the third stage of World 4, where they are found in large quantities. They can be defeated the same ways as a common enemy; jumping on its head, freezing them with a Ice Flower or wearing a Penguin Suit, attacking it with a Fire Flower, or by running into it with a Starman. The sand balls can also be defeated, but only by jumping on them, as ice balls and fireballs are ineffective. They behave very similarly to Spikes.
New Super Mario Bros. U
Huckit Crabs reappear in the Wii U game, New Super Mario Bros. U. This time, they throw rocks. This is similar to the Stone Spikes, who used to throw rocks, but now throw sand balls. Also, the rocks they throw can be raised in elevation by a Water Spout.
Mario Party series
Mario Party 9
In Mario Party 9, Huckit Crabs appear on the Blooper Beach stage. When the player lands on an Event Space, which appear after traversing half the board, the crabs on a pirate ship fire their cannons, which turn any Mini Stars into Mini Ztars and vice versa. Several scattered Huckit Crabs also appear on the board.
Mario Party: Island Tour
Huckit Crabs appear in various minigames in Mario Party: Island Tour.
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