Valgrmir the Scourge, Warlock of Tiamat

Boss Monster. Valgrmir takes full turns at initiative steps 20 and 10 or 15 and 5 and partial turns (movement or action) on initiative steps 15 and 5 or 10 and 0. Additionally, his HP is slightly increased and his damage is slightly decreased. 

Empowered Attacks. Valgrmir's weapon attacks are treated as magical for the purposes of bypassing resistance or immunity.

Great Weapon Fighting (3 day). Whenever Valgrmir rolls a 1 on an attack roll, he can reroll the attack. He must use the new roll.

Magic Resistance. The fire giant king has advantage on saving throws against spells and other magical effects.

Siege Monster. Valgrmir deals double damage to objects and structures. 

Innate Spellcasting. Valgrmir is a [9th] level spellcaster. His spellcasting ability is Charisma (spell save DC 17, +7 to hit with spell attacks.) Valgrmir can innately cast the following spells, requiring no material components:

At will: detect magic, fireball,  fire shield, searing smite, 

3/day each: command, stinking cloud, misty step

1/day each: fire storm, wall of fire, prismatic spray, meteor swarm

Multiattack. Valgrmir makes two attacks.

Greatsword. Melee Weapon Attack: +11 to hit, reach 10 ft., one target. Hit: 24 (3d10 + 8) slashing damage.

Fireshield. Melee Weapon Attack: +11 to hit, reach 5 ft., one target. Hit: 16 (2d10 + 5) slashing damage plus 5 (1d10) fire damage.

Molten Rock. Ranged Weapon Attack: +8 to hit, range 60/240 ft., one target. Hit: 25 (3d8 + 7) bludgeoning damage plus 5 (1d8) fire damage.

Fire Breath. Valgrmir exhales fire in a 15 ft. cone. Each creature in that area must make a DC 15 Dexterity saving throw taking 20 (3d10+4) fire damage on a failed save, or half as much damage on a successful one. 

Fling. Valgrmir tries to throw a small or medium creature within 10 feet of it. The target must either succeed on a DC 18 Dexterity saving throw or win a Contest of Strength (their choice), or be hurled up to 60 feet horizontally in a direction of the Valgrmir's choice and land prone, taking 1d8 bludgeoning damage for every 10 feet it was thrown. Additionally, this can be a disadvantaged Ranged Weapon Attack: +8 to hit, range 60 ft., one target. Hit: X damage where X is the amount of damage the thrown target took. Both are knocked prone.

Shield Charge. Valgrmir moves up to his speed in a straight line and can move through the space of any creature smaller than huge. The first time he enters a creature's space during this move, he makes a Fireshield attack against the creature. If the attack hits the target must also succeed a DC 20 Strength saving throw or be pushed in front of the shield for the rest of this move. If a creature fails this check by 5 or more, it is also knocked prone and takes 17 (3d6 + 7) bludgeoning damage. 

Fireshield. When a creature misses Valgrmir with a melee attack he can use his reaction to make a Fireshield attack against that creature.