I'm preparing for running my first campaign (Storm King's Thunder) and I've got most of the basic information down in terms of running the campaign with the information provided but I wanted to add a little extra mechanics for the players to interact with if they so choose. I am especially fond of the idea of a Mephistopheles type demon presenting himself to the party and offering seemingly benign boons that have unintended consequences. I am worried, however, that giving them additional powers without sufficient drawbacks will unbalance the game. Simply signing over a soul seems to have no real in-game consequences that I can think of other than not being able to be resurrected after death.
I feel like a deal will need to have Boons, to tempt characters; Conditions, to make them feel like the deal had consequences; and Punishments, if the characters do not follow the conditions. Below are some examples I have come across of the three aspects of the deal laid out.
- Life Insurance - After failing 3 death saving throws, the character gets 1 free instant Revivify. Can be renewed after Life Insurance is consumed, at a greater price
- Get 3 luck dice (d20) to add to attack rolls, an ability checks, or saving throws. Must be used before outcome is determined. After luck dice is rolled, DM rolls d20 on 19-20 Luck dice value does not effect roll and die is consumed. Die can be regenerated by committing moderately evil acts (ex. destroy a merchant's goods, desecrating temples, rob an orphanage, etc.)
- One use of your voice at any time.
- Collect on another contract made several decades ago. The terms of this contract remain unknown. The mortal who signed the first contract is advanced in years and either doesn’t remember the contract due to their memory failing, or starts begging that there is still time.
- The fiend picks up a small rock off the ground and enchants it with a spell you cannot discern (on a successful Arcana check or casting of detect magic, you realize it's from the Divination school). The fiend then demands that you always keep this rock on your person. You are magically bound to this: if the rock is left behind or discarded, it returns to your pack whenever you aren't paying attention. The rock is always there and tends to get in the way, but imposes no mechanical penalties. Rock allows controlling entity to view the location of the holder at all times. Devil can sell or rent out scrying abilities as they see fit.
- You pay with your mortal time, making you age rapidly into an old person, grey hair (and beard) with old skin and muscles within the next day. Reduce either Strength/Dexterity/Con by 2, or any two by 1.
- From now any gamble you make results in an unwanted outcome
- The devil send to collect on your debt he sends a champion (packs of lesser demons, another person who made a deal, etc.) to kill you
- One of their eyes. Results in -2 penalty on Perception checks.
I have not fully fleshed out each detail and would like to hear criticisms and ideas to implement for each aspect.