Arceus (Pokemon)

Tether to Creation. If Arceus is reduced to 0 hit points, or dies outright, it returns into the power of the celestial entity from which it came. Arceus will return to the plane it was killed in after 100 years. This cannot be prevented except by means of a wish spell, and even then this will only prevent Arceus from re-forming on the plane it was killed on.

Elemental Plates. Arceus has a set of the elemental plates that it can use to power its attacks and defend itself. This allows Arceus to give itself immunity to one damage type at a time, which can be changed at the end of a short or long rest, or as a legendary action or reaction (as described in the legendary actions and reactions sections, respectively). Whenever Arceus deals damage associated with its current elemental plate, it ignores any resistances to the associated damage type, and treats immunity to the damage type as resistance instead. 

Celestial Magic. Arceus' spellcasting ability is Charisma (Spell Save DC 24). Arceus can innately cast the following spells, requiring no somatic or material components:

At Will: plane shift (self only), etherealness (self only), dispel magic (cast at 6th level)
3/Day:  divine word, reverse gravity, fire storm
1/Day: meteor swarm, foresight

Divine Majesty. Arceus cannot be affected by spells of 4th-level or lower unless it chooses to, and has advantage on saving throws against all other spells and other magical effects. In addition, all of Arceus' damage dealt is magical in terms of overcoming resistance.

Legendary Resistance (4/day). If Arceus fails a saving throw, it can choose to succeed instead.

Hyper Beam. Ranged Weapon Attack. +16 to hit, range 120 ft., one target. Hit: 52 (8d10 + 8) force damage.

Zen Headbutt. Melee Weapon Attack. +16 to hit, reach 10 ft., one target. Hit: 19 (2d10 + 8) bludgeoning damage, plus 36 (8d8) psychic damage.

Hyper Voice.  Each creature of Arceus' choice in a 60ft. cone must make a DC 24 CON saving throw, taking 47 (6d12 + 8) force damage on a fail, or half as much on a success.

Judgment (Recharge 5-6). Every creature of Arceus' choice within 120 ft. must make a DC 24 DEX saving throw, taking 90 (20d8) damage of Arceus' current damage type immunity on a fail, or force damage if none are chosen. On a success, the creature takes half damage.

Plate Shift. When Arceus would take damage from a source it can see, it can use its reaction to shift its elemental plate to one of the triggering damage types.

Arceus can take 4 legendary actions, choosing from the options below. Only one option may be used at a time, and only at the end of another creature's turn. Arceus regains all spent legendary actions at the start of its turn.

Divine Body. Melee Weapon Attack. +16 to hit, reach 10ft., one target. Hit: 19 (2d10 + 8) bludgeoning damage, plus 9 (2d8) damage of Arceus' current elemental plate. 

Plate Shift. Arceus chooses a new damage type as its elemental plate.

Gravity Pulse (Costs 2 Actions). Each creature within 30ft. of Arceus must make a DC 24 STR saving throw or take 14 (4d6) force damage and be knocked prone.

Teleport (Costs 2 Actions). Arceus teleports up to 60 ft. to an unoccupied space.

Rend Space (Costs 3 Actions). Arceus teleports up to 60 ft. away to an unoccupied space. Each creature within 15 ft. of Arceus' starting point or destination must make a DC 24 CHA saving throw. On a failed save, the creature takes 17 (5d6) force damage and is teleported, either with Arceus to the new destination or to Arceus' original position, based on which location they were previously.