"You have yourself a deal my dear Miss Granger," Satan said with a low, joking bow "Now In exchange for the lives you have offered in excess, I'll offer you a portion of the power of hell, you'll find that dominion over other spirits comes naturally to you now, as do their languages, I think I'll also give your magical control a bit of a nudge as well, for the number of lives you've sacrificed I'm willing to be that's boosted you to be one of the more powerful witches alive at this point, but you're by no means all-powerful, It's just a more easily controlled more dense version of the magic you're used to. try all the spells you want, the power you wield now should be natural by now. I only ask you entertain me some more on your path of vengeance" and with a Smile and a flash of hellfire Satan was gone.