Arcanist Devil

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

Devil's Sight. Magical darkness doesn't impede the devil's darkvision. 

Spellcasting. The devil arcanist casts one of the following spells, requiring no material components and using Intelligence as the spellcasting ability (spell save DC 15) :

At will : control flames, fire bolt, mage hand, prestidigitation

3/day each : detect magic*, fog cloud*, magic missile

2/day each : darkness*, dispel magic, haste*, invisibility*, sending, suggestion*, vortex warp

1/day each : banishment*, dimension door, synaptic static

*concentration spells

Multiattack. The devil makes three hellfire rays attacks, one of which it can replace by a tail attack.

Tail. Melee Weapon Attack: +6 to hit, reach 10 ft., one target. Hit: 7 (1d8 + 3) slashing damage, and the target substract 1d8 to the next saving throws it makes before the end of the devil arcanist's next turn.

Hellfire Rays. Ranged Spell Attack: +7 to hit, range 150 ft., one target. Hit: 7 (2d6) fire damage and 7 (2d6) necrotic damage.

Infernal Orb (Recharge 5-6). The devil arcanist hurls a magical ball of infernal fire that explodes in a 20-foot-radius sphere centered on a point the devil arcanist can see within 150 feet of itself. The sphere spreads around corners. Each creature in that area must make a DC 15 Dexterity saving throw. A creature takes 24 (7d6) fire damage and 24 (7d6) necrotic damage on a failed save, or half as much damage on a successful one.

Teleport. The devil teleports, along with any equipment it is wearing or carrying, up to 30 feet to an unoccupied space that it can see.

Spell Drain. When the devil sees a creature makes a ranged spell attack or a spell that forces to make a saving throws within 60 feet, it can attempt to drain some of the magic of the spell to empower itself. The creature must succeed on a DC 15 saving throw using the ability score used in casting the spell.

On a success, the spell is not drained and is cast as normal. On a failed check, the caster substract 1d8 to it's spell attack roll, or the target or targets of it's spell adds 1d8 to their saving throw. The devils then gains either 10 (3d6) temporary Hit Points, or regains one use of it's thrice or twice per day spells. If the check is failed by 5 or more, the spell fails, and the devil instead gains 21 (6d6) temporary Hit Points, or regains a use of one of it's once per day spells.