Whitey said:Here's a possible solution. Demon princes/princesses, devil lordlings, and so on grant spells. But they aren't the 'battery' for them, so they don't need divine rank. Vaguely like the Devourer's spell deflection ability, they expend the life levels of those souls consigned to their plane. This gives them - particularly the CE bunch, a reason to traffic in those, and a compelling reason not to just gate in and thrash the Prime. All that arithmetic keeps them busy. The intrigues of who gets to cast what and when makes a hierarchy of both fiends and followers important - something the party may or may not want to get tangled up in.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.