Your party has encountered a Devil. This Devil has been watching your party for months, studying your behaviors...

None, I don't fucking deal with devils, how stupid can you be. The devil knows exactly how smart you are, and it won't approach you if it knows it can't rip you off.

In my younger years I'd manage six or seven in a 24 hour period.

You should consult a physician.

Pretty much youtube.com/watch?v=WBNOXYlYswA

He has a gemstone given to him each day, while the type and size is different each day, the total value is always 500GP, in exchange... The soul of the cleric.

Just don't sign the contract
I mean you have to be pretty clueless to think you can outdeal a devil and nothing they can provide is actually worth it in the long run.

The beast-hunting Ranger becomes the best hunter around, by becoming the biggest predator around. He's miffed, but ok with this.
The bastard who would be king Fighter has his crown.
Either everyone is dead, wants him dead or it's just a crown, no kingdom attached.
The Wild Magic Sorcerer and NPC party face both abstain, they know where this is going.
The Cleric cum Warlock and Sorcerer cum Warlock cum Fire Elemental-Monster-Thing, the plague is gone. Everyone is safe and well, everyone is healed. The survivours can start to head back home to rebuild.
Their bodies, twisted with age, magic-borne pathogens and straight magic are healed. Their powers, borne from the same source, gone as well.
A certain Plague God and a certain Patron of are going to start asking some uncomfortable questions and looking for a little reimbursment on their loans.

No one notices the Devil seemed to include, or even thinks to ask why, our Sorcerer's caged experiment seems to smile a little wider these days, like she still did when her mind was once unbroken.

Honestly, choose the rebellion against the crown option and this seems like a good campaign.

Mahou Shoujo Campaign.
They are signing nothing until they've read it in full, their Teacher, a former Magical Girl herself, has read it, their allies over in the Soul Eating Demons camp has read it in full, the Time Traveling BBEG has read it in full and finally, the defacto leaders of the greater Magical Girl community have read it in full.

Everyone is quite happy with their status quo right now even if this stalemate is a zero sum game in the long run.

Well, the Warrior Summoner is fine, as the only thing she wants nowadays is Matthew Gaul's head in front of her hammer. Which is something she's going to be rectifying awfully soon.
The Mentalist would probably want a meetup with Youko Kyuubei, and there are countless ways that could screw him over, including him being accidentally burned to a crisp by her.
The Weaponmaster is also quite self-sufficient, as she's already got what she wants, which is strong opponents gunning for her.
There is no such person as the Warlock, as he has been technically erased from existence, and is only known to his dragon. And goooood luck dealing with her, mister devil.

This is mostly academic, though, as the moment that devil appeared in front of the party, he'd be scorched by the AURA OF JUSTICE coming off the Warrior Summoner, chomped by her Essence Sheele going DOOMGUY DRAGON MODE, or blown into giblets by the Mentalist and his 700 base Light Damage Psychic Railgun.
The Weaponmaster would ignore him unless he kept getting in her way. Then she'd kick his ass to prove a point.

The ability to have a way to kill the God Machine. Downside being he would probably takes its' place, or even worse, I would

You'd think a devil who's dealing with smart opposites would offer a more transparent and reasonable exchange. It would probably still be immoral since you'd benefit a being made out of pure evil, but you wouldn't necessarily be screwed.

(Unless merely associating with said Evil being has consequences for the afterlife and/or your relationship with your gods.)

Just don't?
Even if its amazing or safe sounding you're risking more than being fucked over temporarily.

Its why I don't get people who are all over succubuses. You're gonna lose your soul faggot, the fuck is one amazing fuck gonna do if its an eternity getting your dick chopped off and going trough highschool again.

Going by campaign here

>Iron Gods
He offers my tiefling trapsmith a chance to be human like they always wanted. Stipulation though is pretty standard for damnation stuff, they'll end up as a fiend again anyways after death. Maybe forces them to make more lethal traps in the meantime.

>PLD
Sorry, already in a deal with some sort of creepy death titan/deity. Maybe he offers to change her bargain but really, it's all the same all around.