How can the agent of a devil "capture" a soul?

Question

Devils always want more souls for the Blood War. Mostly, they get those from lawful evil mortals. But as various lore - and this question What groups of souls go to the Nine Hells according to lore? - make clear, pacts with devils and even magical accidents can also cause a soul to go to the hells.

In my game, one of the party (a Warlock) owes a favour to a devil (their patron). I've decided that this favour will be to "claim" the souls of two NPCs in the town where they've just arrived. The devil in question is Dispater and the town happens to be home to two master blacksmiths, who Dispater would love working in his armouries for all eternity.

Presumably, the most effective way for our Warlock to go about this - if they choose to accept the task - is to try and tempt them with some kind of Faustian bargain so they will agree to sell their souls of their own accord. However, I'm bound to be asked whether there's any other method available to Warlocks or covered in lore about contracts with devils. Are there?

My goal here is to offer some fun role-playing where the Warlock can try and tempt his victims, but if that fails, I'd like a fallback so he's not completely out of options.

Answer 1

A Hellfire Weapon might work.

The Hellfire weapon, from Baldur's Gate, funnels the souls of its targets into the River Styx, converting humanoids into devils.

Any humanoid killed by an attack made with this weapon has its soul funneled into the River Styx, where it's reborn instantly as a lemure devil.

As to how your Warlock would obtain such a weapon, that might become a fun new side-quest.

Answer 2

If the target is evil, A Night Hag's Nightmare Haunting feature and Soul Bag might work.

While a hellfire weapon would send the soul to the Styx, that might not get them to Dis. However, if the target is evil, there may be another option.

According to the description of a Night Hag's Nightmare Haunting feature in MM pg 178:

If this effect reduces the target's hit point maximum to 0, the target dies, and if the target was evil, its soul is trapped in the hag's soul bag.

and in the description Night Hags as Soulmongers:

If the hag has driven her victim to commit evil deeds, she traps its corrupted soul in her soul bag (see the "Night Hag Items" sidebar) for transport to Hades.

Presumably a Night Hag could be persuaded to deliver the soul to Dis rather than Hades.

May open up some role-playing possibilities dealing with a night hag, and the humanoid sacrifice required to craft a soul bag as described in the above-mentioned sidebar.

Answer 3

A warlock has no ability to create fiendish pacts with other mortals—the only fiendish pact a warlock gets to create is their own, with their own patron.

That’s about all we can say with absolute certainty—we have rules for what a warlock can and cannot do, and this isn’t listed among them. That doesn’t mean we can’t fill in some blanks here, based on other things we know.

For example, the lack of any warlock ability that allows making such pacts doesn’t have to mean that the warlock is pointless here—you call them an “agent,” and that’s exactly what they could be, in the legal sense.

An agent, in legal terminology, is a person who has been legally empowered to act on behalf of another person or an entity. An agent may be employed to represent a client in negotiations and other dealings with third parties. […] The person represented by the agent in these scenarios is called the principal.

^{(“agent” in Investopedia)}

So here, the warlock could be the patron’s agent, which means that the warlock can negotiate deals on the behalf of the principal, the patron. That way, a warlock can offer great and wondrous power,™ in exchange for committing one’s soul to Hell, even though they neither have the ability to grant great and wondrous power,™ nor the ability to collect souls. What they are doing is negotiating on their patron’s behalf, and the patron is the one granting the power and collecting the soul. This may, or may not, require the patron’s involvement—that’s up to the patron, how much authority they give the warlock to act unilaterally.

So things can range from the warlock just introducing the third party to the patron, up to the warlock having been given some magic contract that they are able to sign in the patron’s name, binding the patron and the third party together. One expects lower-level, less trusted warlocks to be more of the former kind of thing, while higher-level warlocks might be entrusted with the latter ability. This kind of thing always demands a cost–benefit analysis for the patron—the more independent the warlock is, the more effective they’ll be as an agent, and the less hassle the patron will have collecting those souls, but at the same time, if the agent has been given the authority to sign in the principal’s name, a warlock could potentially sign a contract that the patron does not want, and the patron will be bound by it. Many fiends, no doubt, take a route followed by many people in the business world—the agent can handle all the negotiation and everything right up to the final signature, but that requires the principal’s approval.

Anyway, in all cases, the third party who signs on to a contract is now eligible to take levels of the warlock class with a fiendish patron. (The rules don’t make this a “requirement,” and PCs can be “special” anyway, but then the rules leave a lot of the how and why of leveling up undefined and up to the table.) If you, as DM, like, you can even allow the third party to immediately level up, gaining that 1st level of warlock.¹ This may, however, be a premium feature that the patron doesn’t offer to just anybody. In extreme cases, the patron may even be able to offer several warlock levels all at once—I had a game where a PC died and the player wanted to play as a particular NPC, but that NPC had no levels, so what we did was that they signed a fiendish pact to suddenly get a bunch of warlock levels to make them match up with the rest of the party. We didn’t have a warlock-agent involved, but we could have.

As for the soul, the collection of the soul happens after the death of the third party. That’s the usual nature of a Faustian bargain, after all: enjoy temporal power and prestige, in exchange for an eternity of damnation and suffering.

1. _{Be careful allowing this with PCs, though—if you do, I recommend delaying the new warlock’s next level-up to coincide with the rest of the party reaching the same level, i.e. the warlock is only ahead temporarily}

Answer 4

Depending on the characters level, the spell Soul Cage is used to capture someones soul:

This spell snatches the soul of a humanoid as it dies and traps it inside the tiny cage you use for the material component. A stolen soul remains inside the cage until the spell ends or until you destroy the cage

The character would then have to find a way to actually deliver the soul to the devil within the spells duration of 8 hours.

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If the character is level 14 or higher, they can also use their ability "Hurl Through Hell" (The Fiend patron) which would send the target straight to hell (you would have to homebrew that the devil can actually capture the target while passing through, since this is not mentioned in the description).

When you hit a creature with an attack, you can use this feature to instantly transport the target through the lower planes.

Answer 5

Frame challenge: You don't need a fallback

You heavily imply that you're the DM. As a result, those blacksmith NPCs are under your control. You can simply roleplay the scenario such that the persuasion is infallible.

This also applies to other scenarios. As a DM you have the ability to skip dice rolls. Feel free to make use of it whenever it's beneficial to the story and the game experience.

Update: I've been informed that this is more a case of "I want to give him other options if he comes up with a persuasion I'm not willing to let pass", rather than "I want to make sure the opportunity isn't ruined by a bad dice roll". I'll still keep the answer for future readers, as the "as a DM, I'm obliged to roll skill checks" fallacy is rather common.

Answer 6

Perhaps some sort of hellfire they could use in their forge.

The benefits would be that the fires burned without consuming fuel and the skill checks made by the Master Smith would be made with Advantage.

The "cost" would be that the Smith must call on Dispater daily (ie Pray) for the fire to last; and that making the skill check with Advantage requires that his apprentices and assistants that aid with the skill checks must be exhausted.

With both smiths having the benefits, it will likely reduce the chance that one will decide to stop calling on Dispater, as that will leave his competitor with the Advantage and lack of fuel costs.