Can a demon make a soul pact with Supernatural entities? My gut instinct says no, they can make pacts but not soul pact, but I haven't confirmed this. I'm primarily interested in Vampires but it doesn't seem unreasonable to try to cover all the splats.
p194 of Demon the Descent
Supernatural beings can sign away their souls to demons, but it doesn’t benefit the demon much. When the demon claims the being’s soul, the demon suffers aggravated damage equal to the supernatural being’s Supernatural Tolerance (Blood Potency, Gnosis, etc.) as the being’s power is converted to Aether and burns off. Even then, the demon only assumes the being’s identity…but as a human being. If she claims a vampire’s soul, she takes that vampire’s name and face, but is not undead, does not drink blood, and does not necessarily know the intricacies of vampire society.
There are of course rules for mimicking powers...
queue "I want to be human again" pact.