Galethorn said:
I don't like that the DC to resist it is a fixed 15.
Before you change anything, think.
Take a careful look at the average Fort saves of Grim Tales characters.
This ain't no D&D-- lower saves across the board and no cloaks of resistance lying about.
Boil it all down and what do you have?
Let's say you manage to get yourself up to a +12 Fort save. (Try it out, see exactly what that would take.)
You only risk dying on a 1 or a 2.
Even a 10% chance of dying to a failed MDT save is pretty high.
Think about it.
Most players I know wouldn't even risk a 10% chance of spell failure for their wizard.
So why would you want to play a character with a 10% chance dropping and dying-- with death, in all likelihood, a permanent situation?
Leave the Fort save DC alone, and use the Mooks rule (enemy mooks always automatically fail the Fort save). This will make the enemy drop and die as expected, and protect the heroes, while still preserving some sense of danger.
And it doesn't get any better as you go up in levels. Yes, your Fort save improves. You'll "improve" to the dreaded "Just don't roll a 1..." situation. That doesn't make losing a very high level character any easier.
Trust me, there's not much fun in raising the Fort DC. It will please only the DM.
Wulf