Many who seek to gain power in Hell resort to pacts. Convincing demons to lend their power is tricky, you must be able to discern the drawbacks of such. For every pact may lend power, they always come with drawbacks as well. However, Pact Masters are far and between, easily being able to tell good deals from bad deals. Some may be able to fully negate a drawback if they have the charisma required.
You are able to make pacts with Demons, Daemons, or Devils. By convincing or forcing entities to give you a pact, you are able to gain a feature they give you. You may have 2 pacts at one time. These pacts may enhance different aspects of the game, combat, weapons, roleplay etc; depending on what you make a pact with. Many pacts also come with a drawback as well. (These pacts are not related to the Devil Dealer subclass' pacts.)