Adult Starlight Dragon

Amphibious. The dragon can breathe air and water.

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

Spellcasting. The Starlight Dragon is a spellcaster. Its spellcasting ability is Wisdom (spell save DC 21, +10 to hit with spell attacks). The Starlight Dragon has following spells prepared:
1st level (4 slots):  Magnify Gravity, Guiding bolt
2nd level (3 slots): Flaming sphere, hold person
3rd level (2 slots): Pulse Wave, daylight
4th level (2 slots): Gravity Sinkhole, gate seal
5th level (1 slots): wall of light
6th level (1 slots): Gravity Fissure
7th level (1 slots): crown of stars

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: 18 (2d8 + 8) piercing damage and (2d6) radiant damage. 

Claw. Melee Weapon Attack: +15 to hit, reach 10 ft., one target. Hit: 16 (2d6 + 8) slashing damage and (2d6) radiant damage.

Tail. Melee Weapon Attack: +15 to hit, reach 20 ft., one target. Hit: 20 (2d8 + 10) bludgeoning damage and (2d6) radiant 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 21 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.

Breath Weapons (Recharge 5–6). The dragon uses one of the following breath weapons.

Starfire Breath. The dragon exhales starfire in a 90-foot cone. Each creature in that area must make a DC 21 Dexterity saving throw, taking 24 (5d10) fire damage and 24 (5d10) radiant damage on a failed save, or half as much damage on a successful one. On a failed Dexterity saved a creature must also make a DC: 21 con save or become blinded until the end of the dragon's next turn.

Gravity focusing breath. The dragon exhales a 90-foot line of dark energy. Each creature in that line must make a DC 21 Dexterity saving throw, taking 38 (8d10) force damage a on a failed save, or half as much damage on a successful one. On a failed save a creature experiences gravity at an amplified degree causing the creature to have their movement speed halved and they get disadvantage on STR and DEX saves and checks.

Gravitational attraction. The dragon can pull one creature effected by changed gravity can pull a creature up to 20 feet towards the dragon.

he 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 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 15 feet of the dragon must succeed on a DC 22 Dexterity saving throw or take 17 (2d6 + 10) bludgeoning damage and be knocked prone. The dragon can then fly up to half its flying speed.