Aspect of Entropy

Vile Damage: Each point of Vile Damage reduces Max HP by 5 points. Can only be recovered by casting a Greater Restoration or Wish spell. 
Atropus is as much a place as it is a being. It is a small moonlet spinning through the void, waiting to be ensnared by the pull of the planets it nears. To those on the surface of the chosen world, the elder evil appears as a speck in the sky. At night it is almost invisible, blending in with the darkness, but during twilight and dawn, it looks like a moving pinhole of darkness.
As it draws closer and its sign intensifies, it grows, expanding from a tiny dot to a small disk until it dominates the sky. Pitted and slick with the black slime of the putrid amniotic fluid of its birth, it hangs above, always drifting away from the light of the sun and lurking overhead when the sun has fled. It has the appearance of a huge chunk of black stone, but from certain angles, it looks like a great hairless head, black eyes glassy and soulless. Atropus has no understandable personality and no inclinations other than craving the destruction of all living things.
This rock is not uninhabited: Undead conjured from the darkest nightmares infest it. These horrors claim the craters for themselves, flitting through the shadows, ravenous for the energy of the living. The master of them all is the focus, an extension of Atropus’s will. The focus is a headless, human-shaped creature with flesh fossilized during Atropus's endless roaming through the cosmos. Closer inspection reveals that its foul body shares the same hideous coating that wells up from the rents and fissures on the moonlet’s surface. 

When the moonlet descends to consume a planet, it first sends down a vanguard: The Aspect of Entropy. Connecting via a beam of pure solid darkness it begins to absorb the energy of the planet. The Aspect guards this pillar and sustains it and helps it advance to eventually consume the planet. For 20 miles surrounding the pillar the land becomes and behaves as if its on the surface of the moonlet. Below are the lair actions and Regional effects of being near the pillar. 

Lair Actions
Connecting the surface of the moonlet directly to any planet it decides to consume the aspect can control the moonlet of Atropus and the area its connected to, itself to take lair actions. On initiative count 20 (losing initiative ties), the aspect takes a lair action to cause one of the following effects; the aspect can't use the same effect two rounds in a row:
The aspect innately casts the earthquake spell (save DC 25), requiring no components. This earthquake lasts until initiative count 20 of the next round, and does not require concentration to maintain. Negative energy erupts from any fissure created by the earthquake spell, requiring any creature in or above them to make a DC 25 Constitution saving throw. A creature takes 16 (3d10) necrotic damage on a failed save, or half as much damage on a successful one. 
The aspect chooses a point within 100 feet of it. The moonlet then warps the space immediately near it, centered on this point. Each creature within a 30-foot-radius of the point must make a DC 25 Charisma saving throw. On a failed save, a creature is teleported to an unoccupied space within 90 feet of the aspect. That space must be on the ground or some other horizontal surface, but can also be the bottom of a fissure created by the earthquake spell.
The Aspect can cause the moonlet to generate a sphere centered on a point it chooses within 150ft of itself. The sphere can have a radius of up to 40 feet. The area within this sphere is filled with magical darkness and crushing gravitational force. For the duration, the sphere’s area is difficult terrain. A creature with darkvision can’t see through the magical darkness, and nonmagical light can’t illuminate it. No sound can be created within or pass through the area. Any creature or object entirely inside the sphere is immune to thunder damage, and creatures are deafened while entirely inside it. Casting a spell that includes a verbal component is impossible there. Any creature that enters the sphere’s area for the first time on a turn or starts its turn there must make a DC25 Constitution saving throw. The creature takes 8d10 force damage on a failed save, or half as much damage on a successful one. A creature reduced to 0 hit points by this damage is disintegrated. A disintegrated creature and everything it is wearing and carrying, except magic items, are reduced to a pile of fine gray dust.

Regional Effects
The moonlet of Atropus is a barren, unforgiving wasteland of dread and despair, littered with undead, star spawn aberrations, and debris picked up from the countless worlds it annihilated. The following effects take place on and within 60 feet of the moonlet or its connection point: 
The moonlet remains on the dark side of the world, keeping the planet between it and the sun. As such, the moonlet is in total darkness. The moonlet has a thin atmosphere permeated by a field of negative energy. It is not breathable, and creatures that suffocate in it are overwhelmed by the stench of rotting flesh. 
Due to the moonlet's low gravity, creatures have their walking speed increased by 5 feet, only take 1d4 bludgeoning damage for each 10 feet they fall, and have their carrying capacities doubled.
Creatures take 1 necrotic damage for each minute that they spend on the moonlet. This damage cannot be reduced by resistance to necrotic damage. Constructs, star spawn, and undead are immune to this effect. A creature that isn't a construct, star spawn, or undead that reaches 0 hit points dies instantly, rising as a zombie after 1 minute if nothing raises it beforehand. Such a creature cannot be restored to life by any means.
The amount of hit points restored by magical healing is halved. Spells and effects that attempt to restore life to dead creatures have no effect. Spells that raise undead can animate or target twice as many creatures and take effect for twice their normal duration.