Johannes Cabal the Necromancer by Jonathan L. Howard

Many years ago, Johannes Cabal sold his soul to the Devil in return for the dread secrets of necromancy. All well and good, but now Cabal wants it back. Surprisingly, that’s not a problem either, all he has to do is find one hundred people to sign their souls over. And he only has a year to do it.

Luckily if you’re willing to sell your soul for forbidden necromantic knowledge, getting others to forfeit theirs isn’t going to be much of an issue.