Whirlwyrm

The whirlwyrm can hold its breath for 30 minutes.

The whirlwyrm makes two attacks: one with its bite and one with its tail.

Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: 21 (3d10 + 5) piercing damage, and the target is grappled (escape DC 16). Until this grapple ends, the target is restrained, and the whirlwyrm can't bite another target.

Melee Weapon Attack: +8 to hit, reach 10 ft., one target not grappled by the whirlwyrm. Hit: 14 (2d8 + 5) bludgeoning damage. If the target is a creature, it must succeed on a DC 16 Strength saving throw or be knocked prone.