usually the main reason for me to use faceshift mask is to have a flesh sacrifice on my undead elf. and that's probably the only reason. cuz I've completed the game even without using it a single time during the run.
so it's definitely not mandatory.
also most of the persuasion checks can be solved either by high persuasion skill(my mage passed str checks with ease, even though her str is 5) or by simply killing everyone who disagree with you.
same with a mirror. at first it seems that having 5 in barter, persuasion and etc is a great thing. but in reality you don't need all of it. just think your build.
if you're playing with 4 heroes you can use your main to have persuasion5(cuz he'll be the one who will speak the most), someone to have thievery5(to pick few locks you can't destroy, and the money you'll get from stealing will allow you to skip leveling barter at all), someone with lucky charm(for free loot, not needed at all, but very useful once you get past 6) and the last one with loremaster(mainly for monster's stats, cuz you can identify at the traders).
stealth is useless. and telekinesis is cheesy. so you don't really need to invest in them.
so with setup like this you'll never need to go to the mirrir ever. unless you'll be bored with your build
