Immolate the Sould does significant bonus damage based on the targets corruption points, but I cant find anything in the books on how múch corruption different enemies should have. So I was wondering what level of corruption would you would say was appropriate for the average chaos cultist, a sorcerer, or a chaos space marine.

Also, how would you judge the power to work on demons? If it wasn't for the fact that it would result in +40 bonus damage, I'd have thought something like a Greater Deamon would have had maxed out corruption, seeing as how they're not immune to having corruption points. I mean how much more corrupt can you get than actually being a demon?

There is an easy to overlook piece of text in the description: "...all living creatures..."

Daemons and machines are not living and so should be immune to this power.

As for the mortal damned, anything up to 99 corruption seems appropriate. A Black Crusade preview notes that 100 corruption is apotheosis or doom (as a chaos spawn) time. An older sorceror, closer to the warp, should have appropriately high corruption while someone relatively new to the ways of blasphemy should have single digit or thereabouts. Bear in mind that during character creation, only the most heinous of events and backgrounds give even 1D10 or 2D10 corruption.

Thanks. I didn't know deamons weren't considered to be living. That helps alot if it's correct though I cant find anything in the Deamonic trait that says they aren't, but then OTOH thats true for the Machine trait as well.

I can't find an explicit reference in Rogue Trader (though the Ebon Geist is described as lusting after mortal life) but p225 of the Dark Heresy corebook describes daemons as "formed of the raw energy of the immaterium itself" and "despise the weaknesses of living beings".