Arcane Owl

Arcane Awareness. The arcane owl knows if it hears a lie.

Sanctum Revival. If the arcane owl dies outside of Mount Celestia, its body disappears, and it regains a new body instantly, reviving with all its hit points in its arcane sanctum.

Magic Resistance. The arcane owl has Advantage on saving throws against spells and other magical effects. 

Inscrutable. No magic can observe the arcane owl remotely or detect its thoughts without its permission. Wisdom (Insight) checks made to ascertain its intentions or sincerity are made with Disadvantage.

Legendary Resistance (2/Day). If the arcane owl fails a saving throw, it can choose to succeed instead.

Mental Demiplane. The arcane owl has created a demiplane inside its own mind. It resembles a massive library, with flying books and infinite bookshelves. While a creature is inside this demiplane, the arcane owl always knows the contents of the creature's mind and can target them with spells. The creature, however, can not communicate or otherwise affect things outside of the demiplane. When a creature makes an Intelligence (History) or an Intelligence (Investigation) check, it has a +3 bonus and Advantage on the check.

Perfect Memory. The arcane owl remembers everything it hears, sees, or perceives.

Multiattack. The arcane owl makes three Eldritch Feather attacks and uses Spellcasting.

Claw. Melee Attack Roll: + 9, reach 10 ft. Hit: 16 (2d10 + 5) Slashing damage plus 18 (4d8) Force damage.

Eldritch Feather. Ranged Attack Roll: + 14, range 120/300 ft. Hit: 8 (1d10 + 3) Piercing damage plus 26 (4d12) Force plus 13 (2d12) Radiant damage. 

Spellcasting. The arcane owl casts one of the following spells, requiring no Material components and using Intelligence as the spellcasting ability (save DC 22, + 14 to hit with spell attacks)

At Will: Detect Thoughts, Detect Magic, Mind Spike, Dimension Door, Guidance, Dispel Magic, Enthrall, Sleep.

3/Day: Dispel Evil and Good, Lightning Bolt (level 7 version), Clairvoyance, Scrying, Telekinesis, Command (level 5 version). 

1/Day: Forcecage, Plane Shift (self only), Reverse Gravity, Teleport, Foresight (cast before combat), Imprisonment.

Banished to The Mind (Recharge 5-6). Wisdom Saving Throw: DC 22, up to 3 creatures or objects that the arcane owl can see. Failure: The creature is banished to the Mental Demiplane. A creature can repeat this saving throw at the start of each of their turns, escaping on a success. 

Antimagic Shriek (Recharge 6). The arcane owl unleashes a wave of magical disruption. A 120-foot radius Emanation of antimagic surrounds the arcane owl. Until the start of the arcane owl's next turn, this area is under the effects of the Antimagic Field spell. These effects do not affect the arcane owl. 

Protective Magic. The arcane owl casts Counterspell or Shield in response to the spell’s trigger, using the same spellcasting ability as Spellcasting.

Legendary Action Uses: 3 (4 in lair). Immediately after another creature’s turn, the arcane owl can expend a use to take one of the following actions. The arcane owl regains all expended uses at the start of each of its turns.

Diving Attack. The arcane owl moves up to half its Flying Speed and makes one Claw attack.

Magical Movement. The arcane owl casts Dimension Door, or Telekinesis.

Self Reflection. The arcane owl teleports to the mental demiplane. While there, the arcane owl can return to the plane it left at any time.