Astral Rift Guardian

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

Magic Resistance: The Arcane Guardian has advantage on saving throws against spells and other magical effects.

Magic Weapons: The Arcane Guardian’s weapon attacks are magical.

Multiattack. The Arcane Guardian makes two Arcane Strike attacks.

Arcane Strike. Melee Weapon Attack: +12 to hit, reach 10 ft., one target. Hit: 20 (3d8 + 6) force damage.

Astral Pulse (Recharge 5–6). The Arcane Guardian unleashes a cone of force in a 30-foot cone. Each creature in that area must make a DC 18 Constitution saving throw, taking 45 (10d8) force damage on a failed save, or half as much on a successful one. Creatures who fail their saving throw are also pushed 20 feet and stunned until the end of their next turn.

Dimensional Anchor (Recharge 5–6).The Guardian targets one creature it can see within 60 feet. The target must succeed on a DC 18 Strength saving throw or be pulled 30 feet toward the Guardian and restrained for 1 minute. The restrained target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

Reality Warp (Recharge 6). The Arcane Guardian distorts the battlefield in a 60-foot radius centered on itself. The Guardian rolls a d6 to determine an effect at the start of each of its turns for 3 rounds (see Reality Warp Effects table).

Reality Warps Table (d6)

1. Gravity Surge: All creatures must succeed on a DC 16 Strength saving throw or be knocked prone and take 10 (3d6) bludgeoning damage. 
2. Spatial Tear: One random creature (including the Guardian) is teleported 40 feet in a random direction.
3. Distortion Field: Ranged attacks against the Guardian have disadvantage until the start of its next turn. 
4. Temporal Flux: Players’ initiative order is reversed for the next round.
5. Planar Echo: A spectral duplicate of the Guardian appears and attacks a random player, dealing 22 (4d10) force damage before vanishing. 
6. Arcane Surge: The Guardian regains 50 hit points. 

The Arcane Guardian can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time, and it can only be used at the end of another creature’s turn. The Arcane Guardian regains spent legendary actions at the start of its turn.

Astral Wings.The Arcane Guardian flies up to 40 feet without provoking opportunity attacks.

Arcane Blink. The Arcane Guardian shifts into the Ethereal Plane until the start of its next turn, making it immune to nonmagical damage.

Arcane Strike. The Arcane Guardian makes one Arcane Strike attack.