Excal-heim
Undead Fortitude. If damage reduces the T-rex zombie to 0 hit points, it must make a Constitution saving throw with a DC of 5 + the damage taken, unless the damage is radiant or from a critical hit. On a success, the T-rex zombie drops to 1 hit point instead. Undead Nature. A T-rex zombie doesn't require air, food, drink, or sleep.
Multiattack. The T-rex zombie 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 T-rex zombie can't bite another target.
 
Tail. Melee Weapon Attack: +10 to hit, reach 10 ft., one target. Hit: 20  3d8+7  bludgeoning damage.