Multiattack. The altisaur makes one Stomp attack and one Tail attack. The altisaur can't make both attacks against the same target.

Stomp. Melee Weapon Attack: +14 to hit, reach 10 ft., one target. Hit: 33 (7d6 + 9) bludgeoning damage. If the target is a Huge or smaller creature, it must succeed on a DC 22 Strength saving throw or have the prone condition.

Tail. Melee Weapon Attack: +14 to hit, reach 20 ft., one target. Hit: 45 (8d8 + 9) bludgeoning damage, and the target is pushed up to 20 feet horizontally from the altisaur.