Hold breathe. The Grugga can hold its breath for 1 hour.
Multiattack. The grudge makes two attacks: one with its bite or swallow and one with its tail. Bite. Melee Weapon Attack: + 6 to hit, reach 5 ft., one target. Hit: 9 (1D10 + 4) piercing damage, if the target is medium or smaller it is grappled (escape DC 14). Until this grapple ends, the target is restrained, and the grugga can't bite another target. Tail. Melee Weapon Attack: + 6 to hit, reach 5 ft., one target. Hit: 8 (1D8 + 4) bludgeoning damage. Swallow. The grugga 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 grugga, and it takes 9 (2d8) acid damage at the start of each of the grugga's turns. The grugga can have only one target swallowed at a time. If the grugga dies, a swallowed creature is no longer restrained by it and can escape from the corpse using 5 feet of movement, exiting prone. Magma blast (Recharge 5-6). The grugga spits a ball of magma at a spot it can see within 50 ft of it each creature within 10 ft of the spot must succeed on a DC 14 Dexterity saving throw or take 22 (4D10) fire damage or half as much on a successful save, flammable objects that aren't being worn or carried catch on fire. the ball remains a hazard and a creature takes 7 (2d6) fire damage if it moves through the objects space, the object radiates bright light in a 5 fo radius and cools down after 1 hour and stops radiating light.
Tail strike. If a melee weapon attack hits the grugga within 5 ft of it, it can make one tail attack as a reaction.