Vampiric Half-dragon Tarrasque Lich

Legendary Resistance. If the lich fails a saving throw, it will succeed instead.

Magic Immunity. The lich is immune to all forms of magic. It can't be sent to another plane of existence or have its form altered against its will.

Phylactery. If the lich dies, it reappears in the space it previously occupied and regains all its hit points.

Multiattack. The lich makes as many Horrifying Rend attacks as creatures it can reach.

Horrifying Rend. Melee Weapon Attack: automatic hit, reach 1,200 ft., 1 target. Hit: force damage equal to half the target's hit point maximum. This ignores resistance and immunity. The target is also blinded, charmed,deafened, frightened,
 incapacitated, paralyzed, petrified, poisoned, prone,
 restrained, stunned, and unconscious forever. The lich regains all its hit points.

Cataclsymic Breath(recharge 5-6).1,000,000 foot long, 5 foot wide line. All creatures in the line die.

Wish. The lich casts wish and ignores all the drawbacks.

The lich never runs out of reactions.

Go first. Trigger: Initiative is rolled. Response: The lich goes first.

Eat Attack. Trigger: the lich is targeted by an attack. Response: It misses.

Eat Effect. Trigger: the lich is targeted by an area effect. Response: it doesn't happen.

The lich has an infinite amount of legendary actions. Only one can be used at a time and only at the end of a creature's turn.

Go away. One creature the lich can see is teleported to a plane of existence of the lich's choice.