I didn't try it so I'm not sure, (this may be spoiler-ish btw) I tried the witch, she told me she would contact me to help protect me from the mind control but never did, so I progressed in the quest and had to give the gem to the Cthulhu guy, BUT before the feast I was sneaking around the corrupted lake and found Xer, befriend him, took him to the village, so he was there during the feast, we can talk to him and there's a option to thank him for a potion, we say that it helped during the encounter with that thing, idk if our character was referring to the Cthulhu thing or something else, but I don't remember taking any potion from Xer, just said it cuz it raised his affection. But my guess is that as I found him before finishing the quest, maybe if I had found him even sooner he would give something to fight that thing? Idk, maybe is not related, or it is, but I can't say for sure as I had made too much progress to back up.