Adult orium dragon

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

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: +13 to hit, reach 10 ft., 1 target. Hit: 17 (2d10 + 7) [piercing] damage plus 4 (1d8) acid damage. 

Claw. Melee Weapon Attack: +13 to hit, reach 5 ft., 1 target. Hit: 13 (2d6 + 7) [slashing] damage. 

Tail. Melee Weapon Attack: +13  to hit, reach 15 ft., 1 target. Hit: 15 (2d8 + 7) [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 17 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.

Vaporous Acid Breath (Recharge 5-6). The dragon exhales acid in a 60-foot line that is 5 feet wide. Each creature in that line must make a DC 17 Dexterity saving throw, taking 44 (11d8) acid damage on a failed save, or half as much damage on a successful one. In the radius of the breath weapon a adult vaporous serpent appears and its initiative order is right after the dragon's. 

The adult orium dragon 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. The adult orium dragon regains spent legendary actions at the start of its turn.

Detect. The dragon makes a Wisdom (Perception) check.

Tail Attack. The dragon makes a tail attack.

Wing Attack (Costs 2 Actions). The dragon beats its wings. Each creature within 10 ft. of the dragon must succeed on a DC 17 Dexterity saving throw or take 13 (2d6 + 7) bludgeoning damage and be knocked prone. The dragon can then fly up to half its flying speed.