Hellfire warlock

A Hellfire Warlock is able to enhance the power of their eldritch blasts by harnessing hellfire, a mysterious magical energy found in the Nine Hells. They often gain this power by interacting with the Baatezu, summoning them in order to make infernal contracts or forcibly capturing and interrogating them.

Abilities
Hellfire Blast: Whenever a hellfire warlock unleashes an eldritch blast, they have the option of converting it into a 'hellfire blast'. The hellfire blast inflicts greater damage than a standard blast, but drains a portion of the caster's lifeforce in exchange. The extra damage inflicted is not fire damage; hellfire burns hotter than any fire normally found on the Prime Material Plane. A warlock cannot utilize hellfire blasts if they are physically unhealthy.

Hellfire Shield: The hellfire warlock may surround themselves with a shield formed from hellfire. The shield provides no protection, but will launch hellfire blasts at any opponent who moves too close to the warlock. The warlock's lifeforce will be drained whenever the shield launches a hellfire blast.

Resistance to fire: A hellfire warlock is able to resist the effects of fire weapons and spells, particularly if they already have some form of fire resistance from their studies as a warlock.

Summon Baatezu: A hellfire warlock may call upon a fiend from the Nine Hells, binding it to their will and forcing it to fight alongside them for a short period of time. The baatezu will likely be angered by the binding process, and when the binding expires it may choose to peacefully return to the nine hells, or attack the impudent warlock who summoned it, often opting for the latter. The best way for the warlock to prevent this is to willingly dispel the enchantment before it expires, forcing the baatezu to return to hell before it can betray them.