Adult Sliver Dragon True Form

Legendary Resistance. If the dragon fails a saving throw, it could choose to succeed instead

True Form. The Dragon does not has its power limited from Io unlike the other dragons so it has access to stronger attacks

Spellcasting. The dragon is a 17-level spellcaster. Its spellcasting ability is 25 (spell save DC 19, +19 to hit with spell attacks). The dragon has following spells prepared:
Cantrips (at will): Any
1st level (at will): Any

2nd level (at will):Any

3rd level (at will):Any

4th level (at will):Any

5th level (at will):Any

6th level (at will):Any

7th level (50 slots):Any

8th level (40 slots):Any

9th level (25 slots):Any

10th level (20 slots):Astroid  

Multiattack . The dragon uses one claw attack and one bite attack.

Bite. Melee Weapon Attack: +19 to hit, reach 15 ft., 1 target. Hit: 305 (6d100+ 5) piercing damage. 

Claw. MeleeWeapon Attack: +19 to hit, range 10 ft., 1 target. Hit: 205 (4d100 + 5) slashing damage.

Tail. Melee Weapon Attack: +19 to hit, range 20ft, 1 target.Hit: 205 (4d100+5)  bludgeoning damage

Frightful Presence. Each creature of the dragon’s choice within 140ft of the dragon has to succeed on a DC25 Wisdom saving throw or be frightened for 1min. The frightened creature can repeat the saving throw at the end of its turns to end the effect on a success. The creature is also immune to the dragon’s Frightful presence for the next 24hours if it has a success on its saving throw.

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

Cold Breath. The dragon exhales an icy blast in a 100ft cone. Each creature in the area has to make is DC24 strength saving throw or take 950(9d100+50) Fire damage or half is much damage on a successful one

Paralyzing Breath. The dragon exhales gas in a 60ft cone. Each creature in the area must make a DC25 Constitution saving throw or be paralyzed for one minute. The can try the saving throw again and end the effect on a success.

The dragon has 3 legendary actions and can use 1 legendary action per turn

Detect. The dragon makes a wisdom perception check.

Tail Attack (Costs 1 Actions). The dragon makes one tail attack 

Wing Attack (Costs 1 Actions). The dragon beats its wings. Any creature within 10ft of the dragon must succeed in a DC25 Dexterity saving throw or take 250(2d100+50) bludgeoning damage and be knocked  prone. The dragon can then fly up to half its flying speed.

The dragon has one mythic action. It could use the mythic action every 30min

 Shining Frost burst (Cost 5 actions). The dragon exhales a shining mega flame in a 100ft cone. Each creature in the area has to make a DC25 strength saving throw or take 1050(10d100+50) cold damage if the target is immune to the cone’s damage type, you roll half the damage despite the immunity.You take half as much damage on a successful saving throw.