So i've been running a few games for a party of 4 PCs.
While things were average on chances of getting hit early and mid level, they are at lvl 9 now.
Their frontliners have flat AC 30 and AC 29 (probably more after spending their money), most enemies, save for sub-bosses and bosses themselves, have a very slim chance of hitting on average. (most only on nat 20, and still not guaranteed, due to below)
Also, anything of having a fair chance of hitting them, is prone to the witch's protective luck hex, which gives a static misfortune effect on enemies' attacks against the party. Crits have been all but prevented with this setup, so far.
Damage effects/spells like dragon breath/fireball have proven somewhat troublesome, but the enemy casters don't tend to live long after getting one or 2 spells off.
They will be lvl 10 after a 1 shot one of the coming days.
So with good to high AC (the cleric pumped his AC to 40 last session) and protective luck active on everyone save the witch herself, what modules (and monsters in general) could still pose a challenge to such a party?