Bluespawn Stormrage Godslayer

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

Magic Weapons. The spawn's weapon attacks are magical.

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

Shield Master. The Spawn chooses the attack action, it can as a bonus action to shove a creature within 10 feet of the spawn.  Strength checks are made to determine how far the shove is.  For every 5 lower than the spawn's strength roll add 5 feet. If the Spawn is subject to a Dexterity saving throw against an effect allows you to take only half damage or no damage if the spawn succeeds the saving throw.

Shock Aura. At the beginning of each of the spawn's turns, each creature within 5 feet of it takes 8 (2d6) shock damage. 

Multiattack. The spawn males two melee attacks and one bite attack.

+2 Greatsword. Melee Weapon Attack: +15 to hit, reach 15 ft., one target. Hit: 25 (3d10 + 9) Slashing damage. 

Bite. Melee Weapon Attack: +13 to hit, reach 15 ft., one target. Hit: 18 (2d10 + 7) Piercing damage, plus 8 (2d6) shock damage.

Shield Slam. Melee weapon attack: +13 to hit, reach 15 ft., one target. Hit: 20 (3d8+7) Bludgeoning damage. Plus Strength save (DC 20) or creature is knocked back 15 ft., if save is 14 less than creature is knocked prone.  If save is less than 4 creature is knocked unconscious.

 Aftershock. A creature that touches the spawn or hits with a melee attack while within 5 feet of it takes 8 (2d6) shock damage.

The spawn 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 spawn regains spent legendary actions at the start of its turn.

Call Lightning (Rechage 5-6), (Costs 2 Actions). The spawn can call lightning from the sky regardless of weather conditions. By the power of Tiamat lightning crashes down centered on the spawn and in a 40 ft. radius all creature's touching the ground take (6d10)  lightning damage. DEX save DC 21 or half damage.

Shield Slam (Costs 1 Action). Melee weapon attack: +13 to hit, reach 15 ft., one target. Hit: 20 (3d8+7) Bludgeoning damage. Plus Strength save (DC 20) or creature is knocked back 15 ft., if save is 14 less than creature is knocked prone.  If save is less than 4 creature is knocked unconscious.

Roar (Rechage 5-6), (Costs 2 Actions). The spawn unleashes a powerful roar. Each creature within 100 feet of the dragon that can hear it must make a Constitution saving throw (save DC 21) or take 11 (3d6) thunder damage and be stunned until the end of its next turn. On a successful save, the creature takes half as much damage and isn't stunned.