Legendary Resistance (5/Day). If Vecna fails a saving throw, he can choose to succeed instead.
Rejuvenation. If Vecna is destroyed, he gains a new body in 1d10 days, regaining all hit hit points and becoming active again. The new body appears within 5 feet of the phylactery on the world of Oerth.
Spellcasting. Vecna is a 20th-level spellcaster. His spellcasting ability is Intelligence (spell save DC 27, +19 to hit with spell attacks). He has the following wizard spells prepared:
Turn Immunity. Vecna is immune to effects that turns undead.
Paralyzing Touch. Melee Spell Attack: +12 to hit, reach 5 ft., one creature. Hit: 10 (3d6) cold damage. The target must succeed on a DC 18 Constitution saving throw or be paralyzed for 1 minute. The target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.
Know Secrets. Ten creatures that Vecna can see within 120 feet must succeed on a DC 21 Wisdom saving throw. If it fails, Vecna immediately learns its entire history, including any embarrassing or vital secrets it might know.
Vecna can take 5 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.
Cantrip. Vecna casts a cantrip.
Move. Vecna moves (walking or flying) up to half his speed. Vecna does not provoke opportunity attacks with this movement.
Paralyzing Touch (Costs 2 Actions). Vecna uses his Paralyzing Touch.
Bone Liquefy (Costs 3 Actions). Vecna makes a melee spell attack (+19 to hit, reach 5 ft.) against one target that has a skeleton. If it hits it must then succeed on a DC 21 Constitution saving throw or drop to 0 hit points as the bones turn to liquid. On a successful save the target takes 42 (12d6) necrotic damage.
Cast a Spell (Costs 3 Actions). Vecna casts a spell from his list of prepared or innate spells, using a spell slot or spending a use as normal.
Soul Drain (Costs 4 Actions). Each living creature within 20 feet of Vecna must succeed on a DC 21 Constitution saving throw or take 35 (10d6) necrotic damage on a failed save, or half as much damage on a successful one. Vecna regains hit points equal to half of the total damage dealt to all targets. If this damage reduces a creature to 0 hit point it dies, if Vecna has a phylactery, the soul gets trapped inside. A soul trapped in Vecna’s phylactery for 24 hours is devoured and ceases to exist. If Vecna’s phylactery is destroyed the soul becomes free and it is returned to the body from where it came from.