Multiattack. The tyrannosaurus makes two attacks: one with its bite and one with its tail. It can’t make both attacks against the same target.
Bite. Melee Weapon Attack: +10 to hit, reach 10 ft., one target. Hit: 33 4d12+7 piercing damage. If the target is a Medium or smaller creature, it is Grappled (escape DC 17). Until this grapple ends, the target is Restrained, and the tyrannosaurus can’t bite another target.
Tail. Melee Weapon Attack: +10 to hit, reach 10 ft., one target. Hit: 20 3d8+7 bludgeoning damage.