Advice for a new mechanic

[Vulspyr]

Hey everyone, I'm currently writing a campaign for 5e where the characters will be journeying through nine circles of hell.

Curently the circles are limbo, wrath, gluttony, greed, pride, lust, sloth, and deception. With one more floor that I haven't chosen a theme for yet. The general idea for the campaign is going to be that the heroes journey through hell and can close the gates that lead to the mortal realm, take over the circles (becoming kings and queens of hell) , become servants to the heads of the circles, or others things if they want to. They are there because they are a mercenary group sent there to close the gates the save the mortal realm, but they obviously don't have to do that if they don't want to.

I am planning on introducing a somewhat floor specific mechanic that will be called temptation. The idea behind it will be that when they commit an act that could easily lead to the sin (such as eating could lead to gluttony if one does not moderate how much they eat when they are in gluttony), or they directly succumb to the temptation (raging in wrath), they need to roll a wisdom check, will save, of a certain difficulty to not succumb to the temptation or to not fully succumb.

An example of how I currently envision it working on gluttony is that when they eat they are required to roll a will save against their current temptation score. If they fail the will save their temptation score will increase. If they fail by more than 10 they fully succumb to the temptation and they are lost to the team, and nothing short of an intervention by a lord of heaven or a lord of hell can save them, and they can't be resurrected because they aren't dead.

If you have an idea of how I could make this temptation thing work on any of the floors without making it unfair, or making it easy would be great. Thanks for any help you provide.

[JeenLeen]

Regardless of what method you use, I think the players should be aware of it or at least a sketch of it (if figuring out how it works is part of what the PCs are doing as well.) In-game, let the PCs be warned that they should avoid the temptation of a given circle when it in, lest they be taken in by the circle.

The basic concept sounds good, but a single Will save to become an NPC is worse than a save-or-die. So that's probably just not fun. They can always roll a 1, after all.
I'd recommend something like penalties. If they do something that would tempt to the sin of a given circle, they have to roll a Wisdom save. If fail, they get a penalty, something like -1 to all rolls (including Wisdom rolls, so more likely to fail again). Such penalties can accumulate, sort of like exhaustion does, and if at the max level (whatever that is), they become an NPC, utterly absorbed into the activity of the given circle.
I'd imagine the penalties represent, at early level, being distracted to a significant degree by the temptation. At higher levels, you are actively engaging in it in some fashion (either physically or mentally), leading to more severe penalties to focus on other tasks. Even for wraith, this could mean having trouble focusing your wraith on one target instead of indiscriminately, so the penalties still apply even in combat.
Note that I'm not proposing what the penalties should be, beyond the lowest being -1 to all rolls. The Exhaustion tables are probably a good guide, but I'd be more severe than they are in their lower levels. (But I do recommend letting a long rest, if avoiding temptation during it, alleviate one level if you meditate or something to rid yourself of tempting thoughts.)

Also, I realize that this benefits those with Wisdom proficiency. That seems realistic, but unfair. Maybe the save should be Wisdom ability modifier + proficiency bonus, so that no classes get penalized more easily for something that's the crux of a campaign. Basically, a Wisdom ability check instead of a Wisdom save.

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In a completely different track: You might like looking at 3.5's Heroes of Horror, for its corruption system. I forget the details, but it had a method of tracking physical and mental corruption. I don't think it was a really great system, but, well, some ideas.

[Vulspyr]

Rolling a 1 results in a regular failure, the plan was to have PC's be able to pick a virtue and when they get to that floor they start at a negative score, or lower than everyone else, and the only way for them to fail was to roll a 1. So rolling a one is not an instadeath, rather it is a regular failure unless the 1 puts them below that 10 range. I was also hoping to add ways for them to lower their score like observing temperance for an entire day will lower it by 2 or something.

I like your penalty idea, and I like the idea of the direction of the wrath being harder to control as the score goes up.

I think the proficiency would partially come from which virtue they have taken.

I was also thinking of adding benefits to the floor, such as everyone can rage on wrath and the benefits of rage would be twice as high and the detriments would be what is normal. The downside would be that failing to properly exit the rage with a save would result in a frenzied rage, and then failing to exit that would result in a loss of control of the character, and having the character rage until they die or are knocked unconcious.

I'll take a look at that corruption system for ideas.

Let me know your opinions.