Ciaran, The Corrupting

Cunning Action. On each of his turns, Ciaran can use a bonus action to take the Dash, Disengage, or Hide actions.

Evasion. When Ciaran is subjected to an effect that allows him to make a Dexterity saving throw to take only half damage, he instead takes no damage if he succeeds on the saving throw, and only half damage if he fails.

Unworldly Riposte. Ciaran can take one reaction per turn, rather than only one per round.

Innate Spellcasting. Ciaran is a 12th-level spellcaster. Its spellcasting ability is Wisdom (spell save DC 16, +8 to hit with spell attacks). Ciaran has the following spells prepared:
Cantrips (at will): Druidcraft, Primal Savagery, Thorn Whip, Resistance
1st level (4 slots): Absorb Elements, Entangle, Longstrider 
2nd level (3 slots): Pass without Trace, Spike Growth, Locate Animals or Plants
3rd level (3 slots): Conjure Animals, Plant Growth, Wind Wall
4th level (3 slots): Blight, Locate Creature, Freedom of Movement
5th level (2 slots): Contagion, Commune with Nature, Insect Plague 
6th level (1 slots): Conjure Fey, Wall of Thorns

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

Magic Resistance. Ciaran's weapon attacks are magical.

Regeneration. Ciaran regains 5 hit points at the start of his turn.

Tree Stride. Once on his turn, Ciaran can use 10 feet of his movement to step magically into one living tree and emerge from a second living tree within 60 feet of the first tree, appearing in an unoccupied space within 5 feet of the second tree. Both trees must be Large or bigger.

Multiattack. Ciaran can use his Frightful Presence. He can then make two attacks with his claws and one with his tail.

Claws. Melee Weapon Attack: +12 to hit, reach 5 ft., one target. Hit: 16 (2d8 + 6) slashing damage.

Tail. Melee Weapon Attack: +12 to hit, reach 10 ft., one target. Hit: 14 (2d6 + 6) piercing damage. The target must make a DC 18 Constitution saving throw, taking 24 (7d6) poison damage on a failed save, or half as much damage on a successful one.

Corrupting Touch. 

Absorb Elements. Ciaran can cast Absorb Elements.

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

Cantrip. Ciaran can cast one cantrip.

Green Stride (Costs 2 Actions). Ciaran can move up to his movement speed without provoking attacks of opportunity.