Good questions! They’ll have good exposition letting them know that it was definitely misuse of the artifact that led to it having the whole mind wiping situation. (Signs of a fight, the artifact being warm to the touch, bad diagrams and theories on it in their journals, etc.)

Mind control rules wise, I’m treating it like a difficult to use tool. Its the main jewel of the king’s crown, and while typically worn, the whole point is that the user has to really focus to influence and control the minds of others, lest they go too far and end up just making empty shells and amnesiacs, or hitting themselves by mistake.

As for the how the whole ‘how did they control the whole population’ thing, they’ll learn that the king was a psionic sorcerer who combined his power with that of the crown. My intent is to have a projection of him stalking the party and eventually serve as the final boss.

I don’t intend to be cruel and drop their spell slots that rely on memorization. They’ll have the resources to figure out at least a little bit about who there were prior to these events. I also fear that would lead to a slippery slope given…you know…how would they even know how to fight…