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

Regeneration. At the start of each of its turns, the dragon regains 4d10+12{"diceNotation":"4d10+12", "rollType":"healing", "rollAction":"Regeneration"} hit points. 

Multiattack. The dragon makes one Bite attack and two Claw attacks.

Bite. Melee Weapon Attack: +12 to hit, reach 10 ft., one target. Hit: 17 (2d10 + 6) piercing damage plus 11 (2d10) psychic damage.

Claw. Melee Weapon Attack: +12 to hit, reach 5 ft., one target. Hit: 13 (2d6 + 6) slashing damage.

Tail. Melee Weapon Attack: +12 to hit, reach 15 ft., one target. Hit: 10 (1d8 + 6) bludgeoning damage. If the target is a creature, it must succeed on a DC 20 Strength saving throw or be knocked prone.

Cerebratic Breath (Recharge 5–6). The dragon projects the reality-warping force of the Far Realm in a 90-foot cone. Each creature in that area must make a DC 19 Wisdom saving throw. On a failed save, the creature takes 49 (9d10) psychic damage, and it is confused (as described in the confusion spell) for 1 minute. On a successful save, the creature takes half as much damage with no additional effects. A confused creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

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

Distort Reality. The dragon alters the perceptions of a creature that it can see within 30 feet of it, causing it to confuse friend and foe. The target must succeed on a DC 19 Wisdom saving throw or use its reaction to make a melee weapon attack against a random creature within reach, other than the dragon. If no creatures are within reach, or the target can’t take a reaction, it takes 11 (2d10) psychic damage.

Tail. The dragon makes one Tail attack.

Collapse Space (2 Actions). The dragon folds the fabric of reality within 60 feet of itself. Each creature in the area, except the dragon, must succeed on a DC 19 Constitution saving throw or take 28 (8d6) force damage and be pulled up to 60 feet toward the dragon. On a success, a creature takes half damage and is not moved.