Actually, if Demi-Fiend is facing an opponent who is immune to negative energy damage, she really has her options cut down in terms of ability to directly deal damage to an opponent.  Her best personal damage options are full attacking with her touch attack and spamming Harm, and both of those rely on negative energy damage.  After that, it's either Vampiric Touch or using Summon Monster IX to call up Vrocks for 20d6 damage, and the latter option requires at least three of the Vrocks to survive for three whole rounds.<br/><br/>Admittedly, when working as part of a team, she can still contribute with Bestow Curse and Charm Monster most of the time, and her Trap the Soul ability is pretty much an 8/day save or die...  But she still has a distinct lack of direct damage capabilities, which will cause fights to drag out for a while when she's working solo.