Soul selling.

[D20ragon]

I need a soul selling mechanic with more then"no resurrection" as a penalty. Please,good people,help me.

[Rubik]

I need a soul selling mechanic with more then"no resurrection" as a penalty. Please,good people,help me.Fiends use souls as food and currency, as well as slaves and fodder for making more fiends. You can also utilize souls as material components in spells, according to the BoVD.

[Wyrm Ouroboros]

I need a soul selling mechanic with more then"no resurrection" as a penalty. Please,good people,help me.

I'd automatically make them radiate (strongly!) the alignment and type of whatever extraplanar being they sold their soul to; I'd also make them take damage according to that alignment and type. If the alignment happens to match their own (likely), then they take the damage twice - and I might ALSO make the second set, from the soul-sale, unavoidable, e.g. no save for half or whatever. A Bane weapon against that type of being would also be Bane against them.

So if a lawful neutral person sold their soul to a devil (lawful evil), he'd have a strong 'lawful evil/devil' aura, he'd take damage from holy weapons or effects as if he were evil, and he'd take 2x damage from chaotic weapons/effects, since he 'is both' lawful neutral AND lawful evil. If he was affected by some damaging magic that targets evil beings (or devils, or extraplanar beings), he'd take the damage as 'being' evil / devil / extraplanar. If he was struck by a weapon that was Bane vs. Devils, he'd take the extra damage to boot, as if he were a devil.

Someone doing a 'detect X' and studying them for a while (3 rounds, maybe) might be allowed to make a Knowledge (Planes) roll to be able to identify the specific identity of the being. If you sold it to someone 'downstairs', a Paladin concentrating specifically on you would be able to make that roll automatically, presuming she has the Knowledge skill.

[Emperor Tippy]

Sell your soul to an entity and you are at its beck and call.

The entity possessing your soul always has line of effect (and is considered to have line of sight if something requires it) to you. The entity with your soul can bypass your spell resistance as if its not even there. You get no save against any ability used against you by the entity with your soul.

Sell your soul and you pretty much make yourself a slave to whomever has it.

Those are house-rules but they are how I would do it.

Note that there should be a differentiation between a soul that is captured or stolen and one that is sold or given.

[Maginomicon]

Fiendish Codex II has Faustian Pacts:

Devils take special delight in corrupting the souls of their enemies, and Faustian pacts have proven to be among the most effective ways to lure mortals astray. Such a contract, negotiated between a devil and a mortal of any alignment other than lawful evil, exchanges the mortal’s soul for any number of possible benefits. Over the centuries, many adventurers have proven themselves susceptible to the temptations inherent in Faustian pacts, because those pacts promise the sort of powers and abilities that adventurers covet.
It goes on from there to talk about the various kinds of Faustian Pacts.

[NichG]

I second Tippy's suggestions. Being able to basically use you like a familiar is already a big bonus to whomever you sell your soul to, and its a good reason in-game that they wouldn't immediately kill you to collect. Better to use you as a no-save scrying focus, hear what you hear, see what you see, drop spells from within you, throw a dominate and use you as a pawn at a critical moment, etc. They may even try to power you up further to make you into a more useful tool.

That said, you do want to encourage the 'I want to get my soul back!' plotlines, so there should probably be some limits. I'd say the limit is mostly going to be that the owner of the soul can't look through all of his possessions all of the time, so basically there's a good chance that 'he's not watching' at any given moment unless its a very important event of some sort - something like a 15% chance per scene of being watched, down to 5% if the owner is a bigshot with thousands of living souls in his treasury.

On the up side, you're probably going to benefit from your owner's SR when it comes to things like Soul Trap or spells that try to take possession of your soul - after all, what kind of fiend lets some upstart steal his property without putting up some kind of resistance?