Aelaraxis

Cosmic Presence.  Aelaraxis's mere presence affects reality. All spells and magical effects within 120 feet of Aelaraxis have a 50% chance of failing, regardless of their caster's level or the effect's power.

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

Celestial Roar.  Each creature within 120 feet of Aelaraxis must make a DC 20 Wisdom saving throw or become stunned for 1 minute. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

Cosmic Strike. Melee Weapon Attack: +15 to hit, reach 30 ft., one target. Hit: 40 (8d8 + 9) force damage.

Aelaraxis can take 3 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. Aelaraxis regains spent legendary actions at the start of its turn

Cosmic Pulse. Aelaraxis releases a pulse of cosmic energy. All creatures within 60 feet of Aelaraxis must make a DC 20 Dexterity saving throw, taking 45 (10d8) force damage on a failed save, or half as much damage on a successful one.

Spatial Distortion. Aelaraxis creates a spatial distortion in a 30-foot radius centered on itself. All creatures and objects in the area must succeed on a DC 20 Strength saving throw or be pushed 60 feet away from Aelaraxis.

Cosmic Beacon (Costs 2 Actions). Aelaraxis creates a beacon of celestial energy that radiates in a 60-foot radius. All allies within this area regain 30 hit points and gain advantage on all saving throws for 1 minute.