You can enter into a pact with a single non-unique demon of your choice over the course of a game. This gives you significant benefits (varying and according to the type of demon) but also major disadvantages for the rest of the game. One major disadvantage for all demons is that it becomes much harder to be in good standing with your god.

Other examples of advantage/disadvantage pairings:

• A +8 damage bonus in exchange for being unable to become fast or very fast
• Being able to cast any non-healing spell in the game in exchange for no natural heath regeneration
• Maxing out an attribute in exchange for permanent reductions in your other attributes