Uvuudaum

Improved Critical.  The uvuudaum's Head Spike scores a critical hit on a roll of 19 or 20.

Magic Resistance. The uvuudaum has advantage on saving throws against spells and other magical effects.

Legendary Resistance (3/Day). If the uvuudaum fails a saving throw, it can choose to succeed instead.

Tenacious Magic. Any attempt to dispel or counterspell a spell or spell-like ability produced by an uvuudaum must roll twice and take the lower result.

Innate Spellcasting. The uvuudaum's innate spellcasting ability is Charisma (spell save DC 28, +15 to hit with spell attacks). The uvuudaum can innately cast the following spells, requiring no components: 

Cantrips (at will): confusion, dimension door, dispel magic, haste, invisibility, lightning bolt, magic missile, mage armor, shield, stoneskin, true strike, web

3/Day Each: chain lightning, cone of cold, disintegrate, dominate person, plane shift, prismatic spray, scrying, teleport, wall of force

1/Day Each: time stop

Confusion Aura. This ability operates continuously, as the confusion spell but with a 30-foot radius. Potential victims can make a DC 18 Charisma save to resist confusion. Those affected by the aura can make a new save every 4 rounds to throw off the effect. Once it has successfully resisted, a subject remains immune to that uvuudaum’s confusion aura for 24 hours.

Regeneration. The uvuudaum regains 20 hit points at the start of its turn. If the uvuudaum takes radiant or fire damage, this trait doesn't function at the start of the uvuudaum's next turn. The uvuudaum dies only if it starts its turn with 0 hit points and doesn't regenerate.

Contingent resurrection (1/Day). The uvuudaum returns to life if it is slain. Once cast, the spell remains quiescent and does not activate until the trigger conditions have been met. Once triggered, the spell is expended. If the uvuudaum is killed (the trigger), it is restored to life and complete health 1 minute later, so long as even a tiny bit of dust remains for contingent resurrection to act upon. A shaft of shadow erupts down from the far realm, shadowing the subject and everything within 20 feet. 

Head Spike. Melee Weapon Attack: +15 to hit, reach 10 ft., 1 target. Hit: 61 (10d6 + 21) piercing damage, and the target's Wisdom score is reduced by 2d4. The target dies if this reduces its Wisdom to 0. Otherwise, the reduction lasts until the target finishes a short or long rest.The uvuudaum regains 5 lost hit points (or 10 on a critical hit) whenever it drains Wisdom, gaining any excess hit points as temporary hit points. An opponent can avoid the Wisdom drain with a DC 20 wisdom save.

Displacement (Recharges after the Uvuudaum casts an Illusion Spell of 1st Level or Higher). As a bonus action, the uvuudaum projects an illusion that makes the uvuudaum appear to be standing in a place a few inches from its actual location, causing any creature to have disadvantage on attack rolls against the uvuudaum. The effect ends if the uvuudaum takes damage, it is incapacitated, or its speed becomes 0.

Time Duplicate (1/Day).The uvuudaum snatches itself from 1 round in the future, depositing this future self in an adjacent space as a bonus action. The uvuudaum’s future self is technically only a possible future self (the time stream is a maelstrom of multiple probabilities), but snatching that future self from 1 round in the future collapses probability, and the possible future becomes the definite future. The uvuudaum and its future self are both free to act normally this round (the uvuudaum has already used up it's bonus action, but it's duplicate hasn’t). The future self has all the resources the uvuudaum has at the moment it finishes casting time duplicate. Because the future self was previously only a possibility, its resources are not depleted as a result of whatever might occur this round (even if the uvuudaum dies this round). Likewise, it doesn’t have any special knowledge of what might occur during this round. Because the future self is still part of the time stream, the round it spends with the uvuudaum is a round it misses in its own future. Because the uvuudaum’s future duplicate is also the uvuudaum, the uvuudaum misses the next round as well. It simply isn’t there. Tampering with the time stream is a tricky business. Here is a round-by-round summary.

Round One

The uvuudaum casts time duplicate, the future self from round two arrives, and both act normally.

Round Two

The future self—the uvuudaum—gets snatched back in time to help the past self. During this round, there are no versions of the uvuudaum present.

Round Three

The uvuudaum rejoins the time stream. The uvuudaum arrives in the same location and condition that the future self ended with at the end of the first round. Any resources (spells, damage, staff charges) the future self used up in round one are gone for real. Record them now. Using this spell to snatch a single future self stretches time and probability to its limit; more powerful versions of time duplicate are not possible. A character cannot bring more than a single future version of itself back at one time, nor can a uvuudaum snatch a version of itself from farther in the future.

The uvuudaum can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature’s turn. The uvuudaum regains spent legendary actions at the start of his turn.

At-Will Spell. Uvuudaum casts one of its at-will spells.

Melee Attack. Uvuudaum uses Head Spike.

Nailed to the sky (Costs 3 Actions)(1/Day). The uvuudaum focuses on one creature within 300 feet, it places the target so far from the surface of the world and at such a speed that it keeps missing the surface as it falls back, so it enters an eternal orbit. Unless the target can magically fly or has some other form of non-physical propulsion available, the target is stuck until someone else rescues it. Even if the target can fly, the surface is 2 to 4 hours away. The target may not survive that long. Depending on the world where nailed to the sky is cast, conditions so far from its surface may be deadly. Deleterious effects include scorching heat, cold, and vacuum. Targets subject to these conditions take 2d6 points of damage each from heat or cold and 1d4 points of damage from the vacuum each round. The target immediately begins to suffocate.