• Magic?
• Mind over Matter?
• Ki power?
• Cybernetic implants?
• Nanomachines?
• Savage barbaric rage?

Thats up to you. What "Trappings" as they call it in that system (or "fluff") your power takes are what truly makes your character and differentiates it from any number of heroes or villains builds that might choose that power. You could have 2 characters with the same powers, but there are still distinctly different from each other and would RP totally differently. On a side note, in that system, you can spend points to advance existing powers or buy a greater variety of them-so characters that have the same powers and are even of the same Character Rank can still play very differently.

[I also make a comparison to Rhine's argument] that Barbarian for example would have been better if it was simply some kind of "Rager" class because he doesnt like people immediately associating his Barbarian with one kind of fluff or idea-"wild tribesman" when in fact it does not have to be the case. Perhaps your character "rages" dude to some acquired PTSD or pain in their past and never even met a tribe, living an urban life? The tribesman is just one trapping for those abilities, just ONE way the class can add to the setting.

Now admittedly Barb is a base class, so you would expect it to fit into a bunch of multiclass combinations. In contrast HFW is a PrC, and PrCs were always intended as world building tools (although I feel all classes are) still, this suggested fluff addition would not change that, but rather fufill that by adding MORE to the setting rather, than taking anything away.

In the same way-I'm NOT trying to replace HFW or Hellfire. HFW's fluff and Hellfire as a substance can STILL remain apart of setting. Essentially, there'd be something akin to an "Advanced Warlock", OR something along the lines of a "Plane Pact/Bound" Warlock PrC Group.

(The latter name comes from the fact that all of these PrCs/Fluff involve the BASIC idea of the warlock forming some pact, or vow to some sort of power group, or group of entities that are Extra-planar provides them with additional power in some form, in exchange for their life force or Con)

Under the "Plane Pact/Bound" PrC Group heading you'd have:

• Hellfire Warlock [Nine Hells]
• Soulfire Warlock [The Abyss]
• Witchfire Warlock [The Feywild]
• Weirdfire Warlock [The Far Realms]
• Saintfire [Positive Energy Plane]
• Ghoulfire [Negative Energy Plane]

Just as Shayla would like, Hellfire remains "a hell thing" as she put it. HFW retains all of its own "Trappings" -the history, background, origins, and what have you; it just gets placed in its own section describing how it applies to the larger PrC Group. Because each of them are different ONLY thematically, they are all mechanically equal but in no way the same.

An alternative organization structure, would be to simply add the information to the bottom of the page, as "Alternate Class Fluff".

The only real mechanical issue there is that Hellfire is a real thing. It's not just something Hellfire Warlocks get to have but it actually exists.. in hell. Whereas there is nothing like it in heaven or any other outer plane. And I want to keep it that way. Hellfire is a Hell thing in all respects. It burns everything and anything.

True-it might be a real thing in Therafim as according to FCII Mesphistopheles has invested all of his resources into developing a bit of a gamble, hoping he might tempt mortals with Hellfire. But in truth- the very existence of hellfire isnt as much a mechanical issue, as a fluff and setting issue.

Its a [fluff and setting issue] as to whether or not you want it (and derivitive things like Hellfire Engines) to exist in your versions of Hell or if you want Hell to even exist in your cosmology. (i.e. Eberrons Shavarath). One of the key things about PrC's is that they were originally created with the intent of being world building tools-and HFW certainly comes out of the box able to add that element to your setting. This does not mean cannot mod its fluff or any other PrC's fluff to use the class mechanically to serve another purpose in your setting.

And even if you didnt change the classes fluff, that does not mean you cannot add other substances or powers of some equivalence to Hellfire to your home setting. Mechanically what you've got when strip it down to just the PURE mechanics of it and get down to the crank and crunch, you've got a warlock PrC that offers:

1. [Enhanced item use]
2. [Increased damage payed with con]; that damage APPEARS as FIRE (which is FLUFF not crunch). That damage is untyped damage that deals full damage to objects.
3. A [Defensive Ability] that uses that same damage.

In my mind, the hard crunch underneath could certainly take and simultaneously exist in many forms without actually stepping on anyones toes on account of the fact that all of those that could have it would come from the Warlock class. (albeit, FCII does suggest means of adapting it for use with Wizard or other classes if you so chose.)

What I'm trying to suggeest is NOT changing HFW-No. What I am suggesting is that alternate PrC's be created for warlock, not anyone else and using the same mechanics. It. Is. Not. HOMEBREW -if thats the issue that makes you concerned. The reason being is that it would have the exact same cold hard crunch and mechanics as the HFW class-so there could be absolutely no mechanical balanceing issues.

NOW-What I'd like to see, is acknowledgement of alternate warlock origins (as described in CArc) and effectively PrC's for each of those origins for the setting without creating homebrew shennanigans/munchkinism/cheeseness that comes with homebrewing things -because under the fluff, its NOT homebrew but alternate fluff for an existing class's mechanics allowing to people to play equally mechanically with very different flavor that reflects the diversity of the class.

What distinguishes say HFW from Starfire Warlock between each other is the fluff.
-Where does this class come from, where are the people from, how do they do what they do?
-What does this untyped damage look like, exactly what IS it?
-Why does the class lose con for using its ability?

The two could meet each other in the street and not recognize each other at all essentially. As I noted 4E actually gave different mechanical abilities to make different warlock origins distinct-what I want to do instead is the keep the mechanics simple, by keeping them the same, but giving different/alternate fluff options to players who want to take their Warlock into a PrC (of which there are few, so I see myself as adding diversity while maintaning balance).

-Hellfire Warlock (Infernal Power)
-Soulfire Warlock (Abyssal Power) Derived this name from the self destructive 'Soul Fire' energy used by Solamiths
-Witchfire Warlock (Dark Fey Power) Thought about Faerie Fire, but thats already the name of a SRD spell
-Weirdfire Warlock (Abberant/Far Realm/Old One/Elder Power)
-Saintfire (Celestial/Positive Power)

Each one WORKS EXACTLY THE SAME MECHANICALLY and CAN ALL be added to Hellfire Warlock PrC page. ITS ALL ONE PrC, but THE ONLY THING that makes these alternatives different is the fluff surrounding them, each one represents a pact with a different power greater than oneself. While Therafim's fluff is closer to 3.5 warlock, in my mind the PrC however very much represents a pact forged with some power. Complete Mage gives an overview on "Arcane Archetypes" and later on in that chapter also discusses the different sources Warlocks may derive their powers from (Devils/Demons/Celestials/Fey/Slaadi) although there can be more. As noted in the Complete Arcane, warlocks often get their power from a bloodline either by having unnatural blood in them, or through a pact made by their ancestors or a pct made by the warlock themselves when they first took the class (as elaborated on in Complete Mage- albeit pacts are considered standard and taken for granted in 4.0 to further differentiate them from Sorcerer which Therafim does not have.)

PrCs are generally not something you're born or forced into, but something a character must choose to become quite deliberately. NOT that it means you always have to choose the same PrC flavor as the origin of your powers. Maybe you're a thematically "Feylock" from your pact or by birth, but you went through the rituals to make a bargain/pact of sorts with Infernal powers later in life to go into the PrC as Hellfire flavor Or vice versa.

-Ghoulfire (Undead)
Note-although the 4 additional examples above are certainly enough, for whatever reason 'Ghoulfire' strikes me as cool sounding. Albeit, undead dont have con scores and cant take con damage, so they have no life to give in exchange. Although…if there were some potent undead power to make a pact with, I can see them wanting mortal life/con energy to feed on. Although theres no general undead group-Falazure is the undisputed dragon god of undeath and according to our fluff all necromancers pay some lip service to him. Perhaps he could grant Ghoulfire to warlocks, which among them would be known colloqially as "The Breath of The Night Dragon" or "Falazure's Fire".
As an alternative, since most of them deal with planes (the Witchfire warlock being the feywilde) you could LOOK at it as Ghoulfire being associated with say, the Negative Energy Plane. SO-

Hellfire Warlock [Nine Hells]
-Soulfire Warlock [The Abyss]
-Witchfire Warlock [The Feywild]
-Weirdfire Warlock [The Far Realms]
-Saintfire [Positive Energy Plane]
-Ghoulfire [Negative Energy Plane]