Beyonder dragon

Amphibious: The dragon can breathe air and water.

Legendary Resistance (5/Day): If the dragon fails a saving throw, it can choose to succeed instead.

Multiattack: The beyonder dragon can use its Frightful Presence. It then makes three attacks: one with its bite and two with its claws.

Bite: Melee Weapon Attack:+ 15 to hit, reach 15 ft., one target. Hit: 19 (2d10 + 8) piercing damage plus 9 (2d8) damage (of the breath weapon type).

Claw: Melee Weapon Attack: +15 to hit, reach 10ft., one target. Hit: 15 (2d6 + 8) slashing damage.

Tail: Melee Weapon Attack:+ 15 to hit, reach 20 ft., one target. Hit: 17 (2d8 + 8) bludgeoning damage.

Dimensional sever (60ft range) (charges: 25/day): The beyonder dragon can send forwards a tail strike in which any enemy hit by it takes 2d8+8 of bludgeoning damage. But also the thing hit has to roll a DC18 DEX save in which (if they fail) they are immediately sent to a plane of the DM's choosing.

Frightful Presence: Each creature of the dragon's choice that is within 120 feet of the dragon and aware of it must succeed on a DC 19 Wisdom saving throw or become frightened 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. If a creature's saving throw is successful or the effect ends for it, the creature is immune to the dragon's Frightful Presence for the next 24 hours.

Adaptive breathe (Recharge 50-100): The beyonder dragon has the ability to change what damage type it inflicts (fire, lightning, frost, poison, acid, radiant and necrotic) in a 200ft by 10ft line. Each creature in that line must make a DC 22 Dexterity saving throw, taking 67 (15d8) damage of that type on a failed save, or half as much damage on a successful one.