Crystalborne Wyvern

Magic Resistance. The wyvern has advantage on saving throws against spells and other magical effects.

Minor Immutability. The wyvern has advantage on saving throws against its form being changed in any way.

Multiattack. The wyvern makes two attacks: one with its bite and one with its tail. While flying, it can use its claws in place of one other attack. It can replace one or both attacks with Fireballs.

Bite. Melee Weapon Attack: +7 to hit, reach 10 ft., one creature. Hit: 11 (2d6 + 4) piercing damage plus 1 fire damage.

Claws. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 13 (2d8 + 4) slashing damage.

Tail. Melee Weapon Attack: +7 to hit, reach 10 ft., one creature. Hit: 13 (2d8 + 4) bludgeoning damage. 

Fireball. Melee Weapon Attack: +7 to hit, range 20/95 ft., one target. Hit: 11 (2d10) fire damage.

Havoc (Recharge 6). The wyvern unleashes hidden arcane energies deep within it that makes it that for the next 4 rounds, whenever the wyvern hits a creature with an attack, the dragon must make a DC 12 Strength saving throw. On a fail the wyvern automatically takes 2 force damage and is stunned until 1 round has passed or until it takes damage or something comes to shake it awake before 1 round has passed. On a success, the wyvern has advantage on all attack rolls and Strength and Constitution saving throws until the end of the spell duration. If the wyvern succeeds on two of these saving throws in a row, all of its attacks deal an extra two die of damage and it has advantage on all attack rolls and Strength and Constitution saving throws until the end of the duration.

Siege Lockdown (Recharge 6). The dragon makes a Fireball attack on a siege weapon or Huge or larger hostile creature that it can see within 60 ft of it. On a hit, the target takes no damage, but must succeed on a DC 16 Strength saving throw or be restrained for 1 minute. While restrained in this way, the target can't take reactions.