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???? is a type of enemy found in Gwarhar Lagoon in Mario & Luigi: Superstar Saga. They can be a Sharkbone, which is a skeletal shark-like creature, or a Sand Cheep, which appears to be a Blurp with a shark fin attached to its back. These enemies always appear in groups that include both Sharkbones and Sand Cheeps, so it is impossible to tell which kind would attack until the very last moment of the creature's attack.

The name "Sharkbone" is actually based on unused enemy name text and appears as the undead shark's name in the Nintendo Power guide. This guide also refers to the Blurp-like fish as Puffer-Cheep or Puffer Cheep, which is actually a different Cheep Cheep form encountered underneath Oho Ocean in the Oho Ocean Seabed (which is, itself, erroneously referred to as Puffy Cheep ). Additionally, the European version of Mario & Luigi: Superstar Saga contains "Sand-Cheep" replacing the equally-unused "Sharkbone" name in the German text. The easy mode hints in Mario & Luigi: Superstar Saga + Bowser's Minions refer to the skeletons as Sharkbones and the Blurp-like fish as Sand Cheeps, without the hyphen.

Sand Cheeps also make a brief appearance in Mario & Luigi: Partners in Time - they are used as projectiles of Shrooba Divers and bounce over the four heroes. The Hermite Crab's shells and Antasma from Mario & Luigi: Dream Team are labeled as "????" in-game, but the name connection is coincidental.

Attacks
The ???? has two attacks, depending on which type it is: Sharkbones burrow under and attack Mario or Luigi for large damage and possible Poison; Sand Cheeps will jump right over Mario or Luigi, but if they jump, they will get hurt. ???? shuffle places each time one of them attacks, making it quite difficult to tell whether an attacker will be above or below Mario or Luigi. Therefore, the Mario Bros. could get hurt by a Sand Cheep, expecting it to be a Sharkbone, and vice-versa. The Sharkbones stick their head out of the sand before attacking, while the Sand Cheeps provide no warning. However, when the brothers perform a regular Thunder Bros. attack on ????'s, and if at least one of them turns out to be a Sharkbone, the affected Sharkbones will immediately attack Mario and/or Luigi, one at a time. In the remake, the tops of any Sand Cheeps are visible for a few seconds at the start of a battle, thus providing more hint as to what to expect.

Trivia

 * Despite some ???? being the "Sharkbone" variety, sharks do not have bones in the real world - their skeletons are made of cartilage.
 * In Mario & Luigi: Superstar Saga + Bowser's Minions, players can tell the difference between the Sharkbones" and "Sand Cheeps, as the Sharkbones are level 25, but Sand Cheeps are level 24.