What makes things difficult? When is a thing impossible?
The nature of a character advantage is that it allows an individual to transcend their threat level — provided that they can figure out how to apply it before they’re overcome by a challenge placed before them.
I’ve been working through types of difficulty, trying to figure out a class that can be applied to any kind encounter — the nature of the difficulty. It is the manner in which an encounter is deemed an obstacle.
This is what I have, presented in a 2d6 table:
12 – untouchable (high defenses)
11 – invulnerable (damage reduction)
10 – unbreakable (high hit points)
9 – inexhaustible (undead; constructs)
8 – impassable (rough terrain; traps)
7 – initiative (first strike; ambush)
6 – inescapable (maneuvering; speed)
5 – overwhelming (minions; swarms)
4 – undetectable (invisibility)
3 – overpowering (high damage)
2 – unavoidable (high accuracy)
There are a couple conceits here that don’t necessarily jive with the standard model of D&D — the first is that undead and constructs here are assumed to be immortal inasmuch as wiping out their hit points only disables them.
These are your regenerating mummies, your reanimating skeletons, or the Terminator. The best you can hope for is to slow them down.
Now that I have this list, I believe when a Mission/Rumor is “complicated” by a player calling for a rest/recovery action — the GM can opt to roll up a difficulty either to complicate an existing encounter or create a new one.