Not understanding what actually happens when the demands are not met.  If say the pact says "should the party fail to ____ it shall forfeit its life" . Does it automatically die, or does the polyhedron just turn black, and now someone has to go kill the offender?

If the terms that are set are "You do this for me or you drop dead if you negate doing this" and the terms are agreed on, the person who did not accomplish said task drops dead. It's a powerful spell in that regard, but the terms have to be agreed upon so the user knows what they are in for when they are casting the spell.

Thanks.  Also, what do you do with the newly black polyhedron? Make necklaces?  :D

I mean, you could. And that could add some interesting flavor to the game. The way that I've been using this in my own games is, the caster who uses the spell keeps the die to know whether the deal has been met or failed. It's an indicator to the caster of the other member's failure to make good on their end of the bargain signaling that the deal will need to be recast with another willing party at some point. Ideally you wouldn't want a lot of black dice, but if you do have a lot I suppose you could engrave numbers onto each side and have a new set of Dnd dice.

Say an NPC agreed to partake in this spell while under the suggestion spell. After the charm ends, the NPC wants out, but now that the pact is binding. Can the NPC get out of the pact in any way? The pact turns into an object. So, what would happen to the pact if the object were destroyed?

Example 1: A thief NPC stole a PC's backpack, which contained the pact object. In the following combat, the backpack and all its contents were destroyed. What happens to the pact? Is it neutralized/dispelled?

Example 2: The BBEG used this spell to force a PC into a bad position (the PC has to do something for the BBEG that the PC doesn't want to do, but the PC doesn't want to get punished for it). Could they find and break it? Or alternately, could they steal it and undo the pact by magical means? (i.e, a spell like Dispell Magic)

Deal Magic is my favorite fictional type of magic, but rule magic needs tight rules. I love this spell. The uses are endless, I'd just like some more details.

Hey! I'd be glad to fill you in on this. 

Starting with the object, it's main function is as an indicator that the pact is either completed or has been nullified by some means. I never considered some third party absconding with the object or it being destroyed. I think in those instances, the one who cast the spell should be able to summon it upon demand. And, in an instance where it appears to have been destroyed, the caster could summon a new item in it's place. 

In instances where other magics were used to force a creature into a pact, I think the pact would still hold. There should be an escape clause where, if the caster can be persuaded, they can negate the magic on their own forcing the object to dissolve similarly to the agreement reaching its intended effect. Basically it's the same idea of tearing up the contract. Otherwise they could still enforce the contract and now you have a story element to build upon. 

IF THE CASTER IS KILLED I think that would also negate the contract so the magic serves to benefit both parties into fair trade to some degree. By agreeing to a death sentence, it puts a mark on the person who participated, but it also puts a mark on the person who casted the spell. It makes both parties targets by the other unless otherwise stated in the terms. 

I love thought experiments like this so if you have other questions, shoot them my way. I'd love to answer them. 

Thank you for your reply, I’m happy with your response and the rules you’ve given.

i would however like to know your opinion on dispelling it with Dispel Magic, by who the spell is worded I’d say it would work (unless the pact is made using a higher spell slot than the Dispel Magic)

do you think the pact should be vulnerable to outside interference?

Example: A wizard and a warlock makes a pact so that the warlock gets access to the wizards magic item storage, while the Wizard gets to speak with the warlocks patron and extend their knowledge. What if a cleric find this out and sneaks into the wizards studies and casts Dispel magic on it? Would that dispel the pact?

since it’s a 3rd level spell, I’d say immunity to outsiders feels very strong.

would you consider bumping the spell up to 4th level? Based on other 3rd level spells, I feel this has the same impact/ value at 3rd level as it does 9th.

Again thank you for replying I’m sure I gave you quite the surprise when I commented on this after all these years :D

(I’m writing this on my phone before I’m going to sleep, so sorry if my wording is weird)

I don't think Dispel Magic would be as simple as expected with this spell. It would more than likely need to be done in three parts.

1. The creature attempting to dispel the contract would first need to be aware that the contract was placed.
2. The creature then has to locate the individuals who agreed to the contract.
3. The creature then has to cast Dispel Magic on both individuals as the magic is more tied to those that made the contract than it is to the object. 

I also think it would need to be done on both individuals to fully sever the magic. Perhaps it would need to be cast on both individuals simultaneously? This is something I may need to think about. Generally I've had it so that regular magics such as Dispel Magic would have no effect on it while playing it in my games because it's a pact magic. It's similar to a pact made by a patron in the fact that it's two parties that are entering an agreement willingly and both of their essences are then tied up in the magics. BUT I will concede that this would not be as powerful as pact magic done by a deific entity so there is some wiggle room here for interpretation of rules. Hmmm.... I think this may need to be something that follows more of the Rule of Cool than the letter of the law for the spell. The intention of this spell is to encourage more RP scenarios as that's how I more heavily play at my table so having something that could just as easily negate such a heavy spell, even if the spell was made to be a level 4 or higher spell, feels like it negates the importance of it to some degree. I may consider rewording it to allow stipulations to break contract doing certain actions but I'll have to consider this. 

And you did give me a bit of a surprise, but I always appreciate a chance to converse with others on mechanics and game design. I love making stuff for this game and am currently getting ready to launch a Kickstarter next month called Skarr Awakened, if you want to check it out as well.