In my story, the villain is planning to release the spirits from the underworld to hunt his enemy. The problem is, I can't find an incentive for the ghosts to actually do this. The villain is at the moment the CEO of the underworld, so he does have a good amount of power, but what do the dead actually want?
I think you may have answered your own question. 'Release' — it's a common conception that most ghosts are in some loop of a routine, day in, day out, the same old haunts/haunting. Release = a chance to go play in the bigger world. I'm sure they'd do their keeper's bidding as a trade for freedom.
Your story, your rules. You define what the underworld and being dead are like, so use that to your advantage. What do the dead do in the underworld? If it's boring, than freedom might be the only incentive necessary. If they can't experience the pleasures they had while living, can your villain give them the ability to do so in exchange for compliance? If so then that might be a good reason for them to do what he wants. Depending on how much focus you put on developing the underworld/afterlife and what direction you take that, you could even simply have your villain pay them in some sort of ecto-currency or give them extra spirit energy or something along those lines.
Non-existence might be preferable to a boring eternity (Even worse if their existence means some form of torture). Maybe he promises to destroy their souls so they can be free from their pointless life in death.
That's a bit darker than I want my story to be. And as of now in my story the dead aren't being tortured, but maybe I could make my villain start doing that to put more emphasis on his evil-ness.
Can he promise them a shot at redemption? A second chance to live so they could fix things they think are mistakes they made in their lives?
I know I'm a bit late on this one, but what about entry to Elysium? (I'm making the assumption that as your story is in the Underworld that it also has other Greek mythologies in place?) If not you could introduce something similar, essentially a heaven compared to the purgatory they've been stuck in. All depends on the story though.
. Actually no, not going with Greek mythologies. Other than the name it really is completely separate from the Greek afterlife.
Hmm, CEO of the underworld has got me thinking. Anyone know off-hand any stories where God's are just business men? I havent developed the idea fully beyond Death being a bounty hunter/tax collector, and Hades banging on a typewriter all day filing through petitions from the dead and approving entry for souls stuck in limbo. I'm positive it could be funny in a Douglas Adams kinda-way, but give me five years first.
