Arkus Malchar

Pit Fiend. Arkus Malchar can turn into a Pit Fiend using an action.

Spellcasting. Arkus is a 9-level spellcaster. Its spellcasting ability is Strength (spell save DC 18, +13 to hit with spell attacks). Arkus has following Wizard spells prepared:
Cantrips (at will): Create Bonfire,  Fire Bolt, Control Flames, Dancing Lights, Mold Earth
1st level (4 slots): Burning Hands, Magic Missile, Unseen Servant, Disguise Self

2nd Level (3 slots): Aganazzar's Scorcher, Continual Flame, Scorching Ray

3rd Level (3 slots): Fireball, Melf's Minute Meteors, Flame Arrows

4th Level (3 slots): Fire Shield, Wall of Fire, Polymorph

5th Level (3 slots): Immolation, Telekinesis, Animate Objects

6th Level (2 slots): Investiture of Flame, Sunbeam, Mass Suggestion

7th Level (2 slots): Delayed Blast Fireball, Prismatic Spray

8th Level (1 slot): Power Word Stun

9th Level (1 slot): Meteor Swarm

Pit Fiend. Arkus Malchar can turn into a Pit Fiend.

Fire Sword. Melee Weapon Attack: +13 to hit, reach 10 ft., 1 target. Hit:  (2d20 +5) fire damage. 

Flame Bow. Ranged Weapon Attack: +13 to hit, range 100/150 ft., 1 target. Hit: (2d20 + 3d6) fire/piercing damage.

Opportunity Attack. Arkus can make an opportunity attack when a hostile creature that he can see moves out of his reach. To make the opportunity attack, he uses his reaction to make one melee attack against the provoking creature. The attack occurs right before the creature leaves his reach.

Arkus can take 3 legendary actions/Day, 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. 

Fire Sword. Arkus makes a Fire Sword attack.

Flame Bow. Arkus makes a Flame Bow attack.

Pit Fiend. Arkus transforms into a Pit Fiend

Arkus can take 1 mythic action/Day.

Meteor Swarm. Arkus uses the spell Meteor Swarm without expending a spell slot.

Power Word Stun. Arkus uses the spell Power Word Stun without expending a spell slot.