Amphibious. The dragon can breathe air and water.

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

These attacks are for toying with an enemy

Multiattack. The 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) acid damage.

Claw. Melee Weapon Attack: +15 to hit, reach 10 ft., 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.

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.

Acid Breath (Recharge 5–6). The dragon exhales acid in a 90-foot line that is 10 feet wide. Each creature in that line must make a DC 22 Dexterity saving throw, taking 67 (15d8) acid damage on a failed save, or half as much damage on a successful one.

These attacks are for ending their hopes and dreams

MultiAttack. can do BOTH OF THESE IN ONE TURN

HellFire: The dragon spits into the air and small balls of green fire come hailing down any creature within 2000 feet of the dragon must make DC25 dexterity save on fail the DM must roll a d20 and based on the number that it lands on you will have the DM will have to roll 3d20 Radiant Damage for each.   

DOOM! for those who survive Hellfire, will bear witness too the Dragon who glows a blindingly bright green as he summons a meteorite the size of the moon toward you and must now get a natural 20 on their next save, if not they suffer 100 d20 true damage neglecting all resistances.

if on the off chance they survive, they will then have to experience the hell that is..

Instant Death: this is simply unavoidable killing your character instantly with no sound, no movement, and no pain. Once done, it is asked that this character sheet be burned on the spot. this will kill the character physically, and the player mentally. ONLY USE TO UTTERLY DESTROY SOMEONES HOPES AND DREAMS

He will grant your party three wishes of any sort, but if they ask him to kill himself or something to that effect, He will laugh manically as he answers "Im not even strong enough to do that" 

The dragon can take as many Legendary actions as it likes

Rift Time And Space.  The dragon can manipulate anything and everything around a creature or multiple creatures at the same time to see whatever he wishes

Make a tea and biscuit.