Altisaur

Colossal Beast. The Altisaur is considered Colossal for its size (on grid: 60 ft. by 60 ft. or larger). This means that its hit points are d20 + 5 [Example: 2d20 + (5 x Con modifier) + (2 x Con modifier)].

Stomp. Melee Weapon Attack: +10 to hit, reach 20 ft., one target. Hit: 33 (5d10 + 6) bludgeoning damage, and the target must succeed on a DC 17 Strength saving throw or be knocked prone.

Tail. Melee Weapon Attack: +10 to hit, reach 35 ft., one target. Hit: 46 (9d8 + 6) bludgeoning damage.

Bite. Melee Weapon Attack: +10 to hit, reach 30 ft., one creature that is Medium or smaller. Hit: 23 (5d6 + 6) piercing damage and the target must succeed on a DC 15 Strength saving throw or be swallowed. While swallowed, the creature is blinded and restrained, it has total cover against attacks and other effects outside the tarrasque, and it takes 38 (11d6) acid damage at the start of each of the altisaur’s turns.

If the altisaur takes 50 damage or more on a single turn from a creature inside it, the altisaur must succeed on a DC 21 Constitution saving throw at the end of that turn or regurgitate all swallowed creatures, which fall prone in a space within 10 feet of the tarrasque. If the altisaur dies, a swallowed creature is no longer restrained by it and can escape from the corpse by using 25 feet of movement, exiting prone.