Buster, the Maw of Blades

Action Surge(1/day). Buster can take on additional action on his turn, except the Magic Action.

Bladed Body. A creautre that hits Buster with a melee attack takes 6(1d10) slashing damage.

Eldritch Strike. Any attack with a weapon Buster makes causes the hit creature to suffer disadvantage on the next saving throw made agaisnt a spell Buster casts untol teh end of his next turn.

Innate Spellcasting. Buster can cast the following spells innately, without requiring material components (DC 16).

1/day: Eyes of Immolation*, Unstable Explosion*

Indomitable(1/day). If Buster fails a saving throw, he can reroll it with a bonus of +11. He must use the new roll.

Mutated War bond. Buster is magically bonded to Black Devourer, and therefore cannot be disarmed, even when incapacitated.

Mutated War Magic. Whenever Buster takes the attack aciton, he can replace one of the attacks with a spell he knows (included in the multiattack.

Regeneration. Buster regains 10 hit points at the start of  his turn if he has at least 1 hit point.

Spellcasting. Buster  casts one of the following spells, using Intelligence as the spellcasting ability (spell save DC 16):

At Will: Produce Flame, Green-Flame Blade, Frostbite, Firebolt,
1st level(4 slots):Thunderwave, Magic Missile, Burning Hands, Snare
2nd level(3 slots): Gust of Wind, Icingdeath's Frost, Continual Flame, Earth Ripple*

 *Spells from Kibble's Generic Spells

Multiattack. Buster makes three attacks with Black Devourer. He can replace one of these attacks with a spell

Black Devourer Melee Weapon Attack: +13 to hit, reach 5 ft., 1 target. Hit: 16 (1d12 + 9) slashing damage plus an additional 7(2d6) necrotic damage. 

Demon Dance(Recharge 5-6). With supernatural grace, Buster moves up to his movement speed, striking every foe he crosses paths with in aflurry of deadly slashes. Each creature he moves within 10 feet of must succeed on a DC 18 Dexterity saving throw or take 27(3d10+9) slashing damage. Buster regains 1d10 hit points for every foe that fails the saving throw.

Second wind(4/Day). Buster regains 17(1d10+11) Hit Points. Alternatively, he can expend a use to add 1d10 to an ability check he would otherwise fail. If he still fails, the use is not expended. He can move up to half his movement speed without provoking opportunity attacks when he does this.

Buster can take 1 Legendary Action, and only at the end of another creature's turn. He can perform 1 of the following legendary actions:

Attack. Buster makes one melee attack.