Apo'oh, the Rift Demon

Legendary Resistance (3/Day). If apo'oh fails a saving throw, it can choose to succeed instead.

Reactive. Apo'oh can take one Reaction on every turn of combat.

Spellcasting. Apo'oh casts one of the following spells, using Charisma as the spellcasting ability (spell save DC 18):

3/day each: banishment, dimension door, scatter

1/day each: plane shift, teleport

Multiattack. Apo'oh makes three slam attacks. 

Arcane Gates. Apo'oh chooses two Large, unoccupied spaces, one space within 60ft it can see, and the other one within 120 feet of it. A circular portal opens in each of those spaces facing a direction of apo'oh's choice,  and remains for 1 minute or until apo'oh takes a bonus action to close both. A portal is open on only one side. Anything entering the open side of a portal exits from the open side of the other portal as if the two were adjacent to each other. 

Planar Rift (Recharge 5 - 6). Dexterity Saving Throw: DC 18, each creature creature in a 20-foot-cone from a point within 60 feet. Failure: 28 (8d6) Acid, Cold, Fire, Lightning, Necrotic, Poison, Radiant, or Thunder damage of apo'oh's choice. 

Hurl Gate (Recharge 5 - 6). Dexterity Saving Throw: Dc 18, each creature in a 30-foot by 10-foot Line from an arcane gate in the direction of it's opening. Failure: The target teleports to the other arcane gate as if it moved through it. Success: The target is moved to the closest edge of the Line emanation. Success or Failure: The arcane gate is moved to the point at the end of the Line emanation. 

Slam. Melee Attack Roll: +10, one creature within 60ft. Hit: 13 (2d6 + 6) Force damage.

Teleport. The apo'oh, along with any equipment it is wearing or carrying, up to 60 feet to an unoccupied space that it can see. If it instead chooses a space within range that is occupied by a willing Small or Medium creature, they both teleport, swapping places.

Teleport. Trigger: Apo'oh is targeted by a melee or projectile attack. Response: Apo'oh takes the teleport bonus action. 

Disrupt. Trigger: A creature attempts to teleport a target or multiple targets within 120ft of apo'oh. Response: Apo'oh can choose to change the destination of the teleport to a point within the range of the original teleport. 

Deflect. Trigger: Apo'oh is targeted by a melee or projectile attack. Response: Apo'oh redirects the attack to a creature of it's choice within 60 ft of itself. 

Slice. Trigger: A creature attempts to move through a portal. Response: Apo'oh closes the portal on the creature, preventing it's teleport, and forcing it to take 30 (12d4) Force damage.