Bluespawn Overlord

Awesome Blow. Before making a melee attack, the bluespawn godslayer may choose to gain disadvantage on that attack. If it does, and that attack deals damage, the target must succeed on a DC 17 Strength saving throw or be knocked 10 feet away from the bluespawn godslayer in a direction it chooses.

Dragonslayer. The bluespawn godslayer has advantage on attack rolls made against dragons or creatures with the dragon subtype.

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

Spellcasting. The [Bluespawn Godslayer] is an 8-level spellcaster. Its spellcasting ability is [Charisma] (spell save DC 18, +12 to hit with spell attacks). The [Bluespawn Godslayer] has following [Sorcerer] spells prepared:
Cantrips (at will): [Thunder Clap], [Shocking Grasp], [Lightning Lure], [Chill Touch], [Light]
1st level (5 slots): [Shield], [Witch Bolt], [Absorb Elements]

2nd level (4 slots): [Mirror Image], [Dragon's Breath]

3rd level (4 slots): [Lightning Bolt], [Thunder Step]

4th level (3 slots): [Polymorph], [Storm Sphere]

Multiattack. The Bluespawn Godslayer can can make three attacks: one with its bite and two with its claws. Or it may cast as spell and make one claw attack.

Claw. Melee Weapon Attack: +15 to hit, reach 15 ft., one target. Hit: 17 (2d6 + 10) slashing damage.

Bite. Melee Weapon Attack: +15 to hit, reach 10 ft., one target. Hit: 21 (2d10 + 10) piercing damage plus 14 (4d6) fire damage.

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

The spawn can take 4 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 3 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.

Roar (Rechage 5-6), (Costs 3 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.

Spellcasting, (Cost 1 Action per spell level). The spawn can cast a spell.