Medium Beast, unaligned
Armor Class 15 (natural armor)
Hit Points 13 (3d8)
Speed swim +30, walk +30
Challenge 1/8
Skills stealth +4
Senses blindsight 30 ft., passive Perception 9
Amphibious. The crab can breathe air and water.
Claw. Melee Weapon Attack: +3 to hit, reach 5 ft., one target. Hit: 4 (1d6 + 1) bludgeoning damage, and the target is grappled (escape DC 11). The crab has two claws, each of which can grapple only one target.
Source: 5e Core Rules · OGL/Open