Byron, all stones

War caster. 

• You have advantage on Constitution saving throws that you make to maintain your concentration on a spell when you take damage.

• You can perform the somatic components of spells even when you have weapons or a shield in one or both hands.

• When a hostile creature's movement provokes an opportunity attack from you, you can use your reaction to cast a spell at the creature, rather than making an opportunity attack. The spell must have a casting time of 1 action and must target only that creature.

Spellcasting. Byron is an 18th-level spellcaster. Its spellcasting ability is charisma (spell save DC 21, +11 to hit with spell attacks). Byron has following Warlock spells prepared:

Cantrips (at will): Eldrich blast, Sword burst, poison spray

5th level (8 slots): Hellish rebuke, witch bolt, hex, misty step, Spray of cards, fly, Vampiric touch, Raulothims psychic lance, Summon greater demon, negative energy flood, Far step

Multiattack. Byron can attack three times with his blood rapier and cast a spellEldri

Blood rapier. Melee Weapon Attack: +13 to hit, reach 15 ft., 1 target. Hit: 26 (2d8 + 6) Bludgeoning damage. 

Drink a potion: Heal 10d4+20 hp (3/LR)

Cat a spell as AOO