Skullcrawler

Hold Breath. The skullcrawler can hold its breath for 30 minutes.

Multiattack. The skullcrawler makes three attacks: one with its bite or tail and two with its claws. It can't make both attacks against the same target. One attack can be replaced by constrict or swallow.

Bite. Melee Weapon Attack: +10 to hit, reach 10 ft., one target. Hit: 33 (4d12 + 7) piercing damage. If the target is a Medium or smaller creature, it is grappled (escape DC 17). Until this grapple ends, the target is restrained, and the skullcrawler can't bite another target.

Tail. Melee Weapon Attack: +10 to hit, reach 10 ft., one target not grappled by the skullcrawler. Hit: 20 (3d8 + 7) bludgeoning damage. If the target is a creature, it must succeed on a DC 16 Strength saving throw or be knocked prone.

Claw. Melee Weapon Attack: +10 to hit, reach 10 ft., one target. Hit: 14 (2d6 + 7) slashing damage.

Constrict. Melee Weapon Attack: +6 to hit, reach 10 ft., one creature. Hit: 16 (2d8 + 7) bludgeoning damage, and the target is grappled (escape DC 16). Until this grapple ends, the creature is restrained, and the skullcrawler can't constrict another target.

Swallow. The skullcrawler makes one bite attack against a Medium or smaller target it is grappling. If the attack hits, the target is swallowed, and the grapple ends. The swallowed target is blinded and restrained, it has total cover against attacks and other effects outside the skullcrawler, and it takes 10 (3d6) acid damage at the start of each of the skullcrawler's turns. The skullcrawler can have only one target swallowed at a time. If the skullcrawler dies, a swallowed creature is no longer restrained by it and can escape from the corpse using 5 feet of movement, exiting prone.