Well, the continued progression of the Hellfire Blast is problematic, but I allowed one of my players to take a version that spaced it out into 1-3-5 abilities, with the ability to summon a hellfire elemental filling in the class feature spaces.
If I recall correctly, a single one at lvl 2, at the cost of con damage per size (1 for a small, 2 for a medium, and 3 for a large. At level 4, you could summon multiple, but you took nonlethal damage equal to the prior mention for each round they're summoned. I'd have to find my notes to be sure, tho.