Bite

Melee Weapon Attack: +9 to hit, reach 5 ft., one target. Hit: 15 (2d8 + 6) piercing damage, and the target must succeed on a DC 16 Dexterity saving throw or fall prone.

Gnaw

When a gnarljak knocks a Medium or smaller target prone, it immediately makes three additional bite attacks against the same target and can move 5 feet, all as a bonus action.