Aspect of Vecna

Eye of Vecna. Vecna can see through solid objects to a range of 30 feet.

Legendary Resistance (5/Day). If Vecna fails a saving throw, he can choose to succeed instead.

Magic Resistance: Vecna has advantage on saving throws against spells and other magical effects.

Sovereign of Undeath. Unless Vecna is incapacitated, he and undead creatures of his choice within 60 feet of him are immune to features that turn undead.

Special Equipment. Vecna carries the Book of Vile Darkness and Afterthought, a magic dagger that, in the hands of anyone other than Vecna, is a +3 dagger.

Unusual Nature. Vecna doesn't require air, food, drink, or sleep.

Ruin of the Arch-Lich (Recharges after a Short or Long Rest). If Vecna would be reduced to 0 hit points, his current hit point total instead resets to 300 hit points, he recharges his Flight of the Damned, and he regains any expended uses of Spellcasting and Legendary Resistance. Additionally, Vecna can now use the options in the "Mythic Actions" section for 1 hour. Award a party an additional 155,000 XP (310,000 XP total) for defeating the aspect of Vecna after his Ruin of the Arch-Lich activates.

Multiattack. Vecna uses Flight of the Damned (if available), Rotten Fate, or Spellcasting. He then makes two attacks with Afterthought.

Afterthought. Melee Weapon Attack: +19 to hit, reach 5 ft., one target. Hit: 12 (1d4 + 10) piercing damage plus 9 (2d8) necrotic damage and 9 (2d8) cold damage. If the target is a creature, it is afflicted by entropic magic, taking 9 (2d8) necrotic damage at the start of each of its turns. Immediately after taking this damage on its turn, the target can make a DC 21 Constitution saving throw, ending the effect on itself on a success. Until it succeeds on this save, the afflicted target can't regain hit points.

Flight of the Damned (Recharge 5–6). Vecna conjures a torrent of flying, spectral entities that fill a 120-foot cone and pass through all creatures in that area before dissipating. Each creature in that area must make a DC 24 Constitution saving throw. On a failed save, the creature takes 36 (8d8) necrotic damage and is frightened of Vecna for 1 minute. On a successful save, the creature takes half as much damage and isn't frightened. A frightened creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

Rotten Fate. Vecna causes necrotic magic to engulf one creature he can see within 120 feet of himself. The target must make a DC 24 Constitution saving throw, taking 96 (8d8 + 60) necrotic damage on a failed save, or half as much damage on a successful one. A Humanoid killed by this magic rises as a zombie at the start of Vecna's next turn and acts immediately after Vecna in the initiative order. The zombie is under Vecna's control.

Spellcasting. Vecna casts one of the following spells, requiring no material components and using Intelligence as the spellcasting ability (spell save DC 27):

At will: animate dead (as an action), detect magic, dispel magic, lightning bolt, mage hand, prestidigitation, slow

3/day each: cone of cold, dimension door, disintegrate, eyebite, invisibility, scrying (as an action)

1/day each: dominate monster, globe of invulnerability, plane shift (self only), power word: kill

Vile Teleport. Vecna teleports, along with any equipment he is wearing or carrying, up to 30 feet to an unoccupied space he can see. He can cause each creature of his choice within 15 feet of his destination space to take 10 (3d6) psychic damage. If at least one creature takes this damage, Vecna regains 80 hit points.

Dread Counterspell. Vecna utters a dread word to interrupt a creature he can see that is casting a spell. If the spell is 6th level or lower, it fails and has no effect. If the spell is 7th level or higher, Vecna makes an Intelligence check (DC 10 + the spell's level). On a success, the spell fails and has no effect. Whatever the spell's level, the caster takes 10 (3d6) psychic damage if the spell fails.

Fell Rebuke. In response to being hit by an attack, Vecna utters a fell word, dealing 10 (3d6) necrotic damage to the attacker, and Vecna teleports, along with any equipment he is wearing or carrying, up to 30 feet to an unoccupied space he can see.

Vecna 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. Vecna regains spent legendary actions at the start of his turn.

Attack. Vecna makes one attack with Afterthought. 

At-Will Spell. Vecna casts one of his at-will spells.

Rotten Fate (Costs 2 Actions). Vecna uses Rotten Fate.

If Vecna's Ruin of the Arch-Lich trait has activated in the last hour, he can use the options below as legendary actions.

Hand of Vecna (Costs 2 Actions). If a creature has a skeleton, Vecna attempts to turn its bones to jelly with a touch of his hand, making a melee spell attack (+19 to hit) against one creature he can see within 5 feet. On a hit, the target must succeed on a DC 21 Constitution saving throw or become paralyzed and fall prone. This effect can only be undone by abilities that remove curses or the wish spell.

Undead Horde (Costs 3 Actions). Vecna conjures undead creatures to fight for him, acting immediately after Vecna in the initiative order. Vecna can summon his choice of four wights, two beholder zombies, or one boneclaw.