Blorbo's Animate Big Dead Thing

Choose the corpse of a large or huge dead creature. That creature rises as an undead version of itself, using the relevant undead or zombie version statblock (such as a Tyrannosaurus Zombie or Frost Giant Zombie) if it exists and the DM deems it appropriate. If no such statblock exists, cut the creature's normal DEX, INT, WIS, and CHA scores in half and change its creature type to Undead. The undead creature cannot speak except in moans, though it still understands any languages it knew in life.

It also gains the Undead Fortitude rule, meaning if damage reduces the 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 zombie drops to 1 hit point instead.

The creature is under the caster’s control and acts on the same initiative. The caster can use a bonus action to direct the creature to move and take actions, or to issue a general command such as to guard a doorway. 

At the start of the caster's first turn after casting the spell, and on all subsequent turns, the caster must make a CHA check equal to 4 + the creature’s CR, or else lose control of the creature, which then becomes hostile to everyone in the vicinity. Outside of a combat situation, the caster is able to maintain greater focus on the spell, and makes this check every hour.To regain control of the creature, the caster must cast this spell on it again.

After 24 hours, if the creature is still animate, the magical power running through it overloads and it explodes. It dies, and every creature within 20ft of it must make a DC 16 Dexterity saving throw or take 6d6 force damage.