Collector of Riftborn

Spellcasting. The [Collector of The Riftborn] is a 13-level spellcaster. Its spellcasting ability is [Intelligence] (spell save DC 17, +9 to hit with spell attacks). The [Collector of The Riftborn] has the following [Sorcer] spells prepared:

Cantrips (at will): [Chill touch], [sorcerous blast], [Poison spray], [True Strike], [mold earth], and [Gust]
1st level (4 slots): [Chaos bolt], [Earth tremor], [sleep], and [thunderwave]

2nd level (3 slots): [detect thoughts], [enlarge/Reduce], and [mind spike]

3rd level (3 slots): [counterspell], [lightning bolt], and [vampiric touch]

4th level (3 slots): [vitriolic sphere]

5th level (2 slots): [wall of stone]

6th level (1 slots): [sun beam]

7th level (1 slots): [plane shift]

Multiattack. The Collector makes three attacks with his Soulreaver Scythe.

Soulreaver Scythe. Melee Weapon Attack: +13 to hit, reach 10 ft., one target. Hit: 26 (4d8 + 8) necrotic damage. If the target dies from this attack, its soul is immediately harvested.

Chains of Despair (Recharge 5–6). The Collector summons spectral chains from the ground in a 30-foot radius. Each creature of his choice must succeed on a DC 22 Strength saving throw or be restrained. At the start of their turn, restrained creatures take 18 (4d8) necrotic damage. A creature can use its action to repeat the saving throw.

Rift Surge (1/day). The Collector tears open a small rift, summoning 1d4 Riftborn horrors (CR 7–10). These creatures fight under his command for 1 minute before vanishing

Harvest Power. If a creature has died within 30 ft. of The Collector this turn, he can use a bonus action to absorb its essence, immediately regaining 20 hit points and gaining advantage on his next attack roll before the end of his next turn.

Phase Step (Recharge 4–6). The Collector shifts partially into the Rift, becoming incorporeal until the start of his next turn. While incorporeal, he has resistance to all damage, can move through creatures and objects as if they were difficult terrain (taking 5 force damage if he ends his turn inside an object).

Fear Incarnate. The Collector targets one frightened creature within 60 ft. That creature must succeed on a DC 22 Wisdom saving throw or become paralyzed until the end of its next turn.

Soul Shield. When The Collector is hit by an attack, he can consume a bound soul (if any are harvested) to reduce the damage by 30. If this reduces the attack’s damage to 0, the attack is absorbed into his aura with a shriek of trapped souls.

Chainslash. When a creature within 10 ft. of The Collector makes an attack against him, he lashes out with spectral chains. The attacker must succeed on a DC 22 Strength saving throw or be pulled 10 ft. toward him and take 13 (3d8) necrotic damage.

Rift Reprisal. When The Collector is damaged by a spell, he can force the caster to make a DC 23 Wisdom saving throw or suffer psychic backlash, taking 18 (4d8) psychic damage and becoming frightened until the end of their next turn.

Deny Escape. When a creature within 60 ft. teleports or attempts to shift planes, The Collector can rip the rift closed. The creature must succeed on a DC 22 Charisma saving throw or the effect is negated, wasting the spell/ability.

Start with 2 legendary actions, but gain +1 action for each RiftBorn creature killed.

Soul beam. (cost 1 Action) Ranged Attack: +3 to hit, range 200 ft., 1 target. Hit: (5d10 + 10) [necrotic] damage.

Soul Judgment. (cost 2 actions) action: targeted player makes a Constitution saving throw with a DC of 18; on failure, the target becomes incapacitated for 3 turns and takes 3d10+5 psychic damage. On a success, the target is knocked prone and takes 3 psychic damage.

Frightening gaze. (cost 1 action) action: targets the whole party. All targets make a Constitution saving throw. If they fail, they become frightened for the remainder of the battle.