From Compendium of Worldly Lore
Hellfire Warlock burns hot and bright by using their own CON as a disposable resource that can be expended to empower the warlock's primary offensive tool, eldritch blast, while gaining some minor defensive boons too.
Role: Spell DPS
Characteristics: Warlock who self-damages to empower their abilities
Source: Fiendish Codex II
Game Rule Information
The Hellfire Warlock has the following game statistics.
Abilities: Constitution to expend for hellfire blast, Charisma for casting, Dex for survivability
Alignment: Any Evil or Chaotic
Hit Die: d6
Starting Gold: N/A
Class Skills
The Hellfire Warlock's class skills are Concentration (Con), Disguise (Cha), Intimidate (Cha), Knowledge (arcana) (Int), Knowledge (religion) (Int), Knowledge (the planes) (Int), Listen (Wis) Search (Int), Spellcraft (Int), Spot (Wis), and Use Magic Device (Cha)
Skill Points at 1st Level: (2 + Int modifier) × 4
Skill Points at Each Additional Level: 2 + Int modifier
Class Features
All of the following are class features of the Hellfire Warlock.
Weapon and Armor Proficiency: A Hellfire Warlock is proficient with Hellfire Warlocks gain no proficiency with weapons or armor
Hellfire Blast Sp: Whenever you use your eldritch blast ability, you can change your eldritch blast into a hell fire blast. A hellfire blast deals your normal eldritch blast damage plus an extra 2d6 points of damage per class level. If your blast hits multiple targets (for example, the eldritch chain or eldritch cone blast shape invocations), each target takes the extra damage. This damage is not fire damage. Hellfire burns hotter than any normal fire.
Hellfire is the creation of Mephistopheles, archduke of Cania. Hotter than the hottest flames of any world, hellfire burns with a white-hot glow and is capable of burning through even the hardest of substances. Hellfire does not deal fire damage, despite its flames. Even creatures with immunity or resistance to fire take full normal damage from these hellish flames. Hellfire also deals full damage to objects, unlike normal fire damage.
Each time you use this ability, you take 1 point of Constitution damage. Because the diabolical forces behind the power of hellfire demand part of your essence in exchange for this granted power, if you do not have a Constitution score or are somehow immune to Constitution damage, you cannot use this ability.
Invoking: At each level, you gain new invocations known, increased damage with eldritch blast, and an increase in invoker level as if you had also gained a level in the warlock class. You do not, however, gain any other benefit a character of that class would have gained.
Resistance to Fire 10 Ex: At 2nd level, you gain resistance to fire 10. This resistance stacks with any resistance to fire you have gained from warlock class levels.
Hellfire Infusion Su: Starting at 2nd level, you can infuse magic items that you wield with the power of hellfire. Whenever you use a charged magic item (such as a wand or a staff), you can apply one of the following metamagic effects to your next use of the item: empower, enlarge, widen, or energy substitution. These effects work just like the metamagic feats of the same name. Using hellfire infusion is a swift action. You can use this ability a number of times per day equal to your Charisma modifier (minimum one). When you infuse an item with hellfire, it glows briefly with fiery symbols that are disturbing to look upon.
Hellfire Shield Sp: Starting at 3rd level, you can call up hellfire to surround yourself with a protective barrier. Whenever someone directs a melee attack against you, you can, as an immediate action, aim a blast of hellfire at that creature. This blast deals damage equal to your eldritch blast (including bonus damage from the hellfire blast ability). This blast automatically strikes the target, which can attempt a Reflex saving throw for half damage (DC 10 + 1/2 your character level + your Cha modifier).
Each time you use this ability, you take 1 point of Constitution damage. Because the diabolical forces behind the power of hellfire demand part of your essence in exchange for this granted power, if you do not have a Constitution score or are somehow immune to Constitution damage, you cannot use this ability.