Would adding daily rolls for insanity to Curse of Strahd be excessive for a party of 6?

Question

I'm planning to run Curse of Strahd for my D&D group after we finish our current campaign. It's a group of 6 players plus the DM. According to the book, six players is the recommended upper limit for the party size.

In keeping with the campaign's theme of gloom & doom, the the book suggests adding Madness from chapter 8 of the DMG. My group likes to use the homebrew Critical Hits Revisited and so I'd use the insanity effects from the last page of that PDF.

• I'm imagining that the way insanity would work is players would roll a d100 Wisdom save after finishing a long rest. I would use a d100 for this one save specifically so that it gives the players a build up where the odds of going insane are low but not insignificant. This would build tension for the players. I don't want the DC to get too hard too soon, which is what would happen if a standard d20 roll were used.
• Each day, the DC would increase by 1. So after a ten day, the DC would be 10 (I'm including the first day to keep the DC equal to the day number). With a group of six, the odds of someone failing the save start to become very good towards the end of the first week.
• I'm not sure yet if I'd have them stop rolling once they failed and acquired an insanity trait or have the DC reset to 0 and start building again. The idea is to produce a sort of "ticking clock." The resulting insanity is almost inevitable so the question becomes a matter of "when" and the exact nature of their insanity, not "if."

My thinking is that adding this element will definitely add a sense of (meta) fear for the players and some interesting RPG/story interaction. But my concern is that, even at the upper limit of recommended party size, this could make things too hard for them. I don't want the entire party to go insane but I'd like some members to pickup some quirks during the course of an adventure.

So maybe instead of increasing the DC, I just peg it to a lower rate.

Is this homebrew mechanic likely to make the campaign too hard and how many in-game days can I expect the campaign to last?

Answer 1

Insanity will happen very quickly

It doesn't matter if you have increasing difficulty or not, eventually (and quicker than you think), every PC will fail.

The name for the probability distribution you are constructing is a Geometric distribution. If \$p\$ is the chance of failing your saving throw (a success withing the definition of the distribution) the expected number of days until you fail is \${(1-p)}\over p\$.

If \$p\$ is 0.1 (10%) then the expected number of days before you are insane is 9 and you have a 50/50 chance of being insane after 7 days. If \$p\$ is 0.01 (1%) it is 99 and you have a 50/50 chance of being insane after 68 days.

Now, you have 6 PCs doing this so with \$p=0.1\$ expect your first insane PC on day 2. For \$p=0.01\$ it will be about day 11.

How long will the campaign last

To go from level 1 to level 10 (as expected) you will need approximately 212 encounters (see Why does the experience-to-next-level not change between some levels?). At 6 encounters per long rest that's 35-36 days of adventuring.

Add a similar number of downtime days and most of the party will be crazy by the end.

Unless they can cure them they will soon be dead

The insanities in your link are brutal, particularly towards the end of the table. Suicidal and homicidal, for example, will soon result in a PC death for the reasons outlined above.