The Devil

You have made a pact with a devil from The 9 Hells, an evil being acting out of a selfish drive for greater power, and demanding you to slay mortals, damning their souls in hellfire to be reborn as Lemure Devils working beneath your patron, further strengthening their power and influence. In exchange for the steady supply of devils you provide, your patron gifts you immense power and an unnatural prowess in combat. Particularly powerful warlocks in service in this way may even be granted limited command of devils, allowing them to summon forth low ranking devils from the lower planes to aid them in combat. Greater still, the warlocks held in the highest regard by these devils are even granted the power to shift into forms reminiscent of greater devils, taking command beneath their patrons. Warlocks with this pact may serve archdevils such as Asmodeus, Dispater, Mephistopheles, and Belial, or even enterprising Pit Fiends working to grow their forces. The 9 Hells are a brutal place afterall, and those seeking positions of power need every advantage they can get. 

Hellfire

Starting at 1st level, you can temporarily cover your weapon in hellfire to increase the power of your attacks. As a bonus action, you can expend one spell slot to coat one wielded melee weapon in hellfire. You can then perform the following actions. 

• Hellfire Strike: You strike a single target with hellfire. When you hit an enemy with a melee weapon attack, in addition to the weapons damage, you deal 2d6 fire damage, plus 1d6 for each spell level higher than 1st, to a maximum of 5d6.

• Hellfire Slash: You slash your weapon in a wide arc around you. Any creature within 5 feet of you must succeed in a Dexterity saving throw or take 1d6 fire damage,  plus1d6 for each spell level higher than 1st, to a maximum of 4d6.

On a hit or 1 minute after casting, whichever comes first, the fire fades. Additionally, if a humanoid is slain by a hellfire strike, you can choose to damn it's soul, funneling it into the River Styx, where it's reborn instantly as a lemure devil.

Additionally at 10th level, any fire damage you do with spells, class features or magic weapons is now hellfire. Hellfire ignores fire resistance and treats fire immunity as fire resistance.

Infernal Warrior

At 1st level, have trained to hold your own in melee combat. You gain proficiency with medium armor, shields, and martial weapons.

Additionally, you learn to speak, read and write Infernal.

Hellish Chains

At 6th level, you are able to bind creatures in hellfire. As an action, you point to a creature you can see within 30 feet, summoning forth burning chains from the ground. The target takes 2d6 fire damage and must succeed on a strength saving throw or be restrained, taking half damage on a success. While bound in the chains, the target takes 2d6 fire damage at the end of each of its turns. The target can repeat the saving throw as an action, breaking the chains on a success. 

If the target is slain while bound, you can choose to damn their soul, funneling it into the River Styx, where it's reborn instantly as a lemure devil.

You can use this ability twice, regaining both uses on a long rest. 

Infernal Summoning

Starting at 10th level, your knowledge of the infernal planes allows you to summon forth devils to do your bidding. As an action, you can summon a maximum of 10 devils at a point you can see within 60 feet. The sum of their CRs must not exceed your summon pool of 5. All summons have their turn directly after yours, and devils of the same type must be grouped together, striking the same target. They remain for an hour or until you break concentration. 

Your summon pool is replenished after a long rest. Additionally at 14th level, your summon pool becomes 5 + your Charisma modifier, and your max number of summons increases to 15.

Infernal Form

Your knowledge of the occult and skill in harnessing it has finally reached its apex, allowing you to temporarily imbue yourself with hellish power, transforming into a powerful fiend. At 14th level, once per day, you can use an action to take a form similar to a Pit Fiend.

While you are transformed, the following rules apply:

• Your Hit points equal 13 x your Warlock level
• Your Strength increases to 26 (+8) and your Constitution increases to 24 (+7)
• You gain proficiency in Strength and Constitution saving throws and you gain a Fly of 60 feet.
• You become immune to Fire and Poison, you gain True Sight (120ft) and lose all known languages except Infernal.
• You become one size larger, your creature type becomes Fiend and you take an appearance similar to a Pit Fiend
• You can attack twice, instead of once, when you take the Attack action on your turn. You ignore this benefit if you already have a feature, like Extra Attack, that gives you extra attacks.
• Lastly you gain a bonus action Tail Swipe as outlined below.
• Tail. Melee Weapon Attack: +14 to hit, reach 10 ft., one target. Hit: 24 (3d10 + 8) bludgeoning damage.

The transformation does not require concentration, and lasts 1d4-1 hours, with a minimum duration of 1 hour. You must succeed on a DC 18 Wisdom saving throw to end it early, and you can repeat the save an hour after the last failed save. Finally, a remove curse will also revert the transformation early if you are willing. Reverting back by any method listed above gives you two levels of exhaustion. Additionally, the power of the fiend clouds your mind as the thrill of battle consumes you. When there are no creatures you deem hostile within line of sight, you must succeed on a DC 13 Wisdom saving throw. If you fail, you must use your action each round to attack the creature nearest to you. If you can make extra attacks as part of the attack action, you use those extra attacks, moving to attack the next nearest creature after you fell your current target. If you have multiple possible targets, you choose one. You can repeat the save at the start of each of your turns, regaining control on a success. Every hour you remain transformed requires another save, going berserk on a fail.