One of the lines regarding this item is a bit ambiguous to me.
Read the thoughts of any creature reflected therein, as long as the creature controlling the mirror is within 25 feet of the mirror, even if those thoughts are in an unknown language.
So, my question is if this is meant to refer to being used in conjunction with the clairvoyance ability that the mirror also gives one. I.E. I watch the throne room, so the king is "reflected" in the mirrors surface. Or is it meaning literally just people standing in front of the mirror? I personally think the first is RAI, but I don't know.
Also, there doesn't seem to be a DC to resist, does this mean that the mind reading cannot be resisted?
My reading is that you don't get the thought reading effect unless the creature is physically standing within line of sight to the mirror.
Given that it's in the list of top ten items by cost, no save seems appropriate.
That just seems so thematically odd though. But I guess RAW that seems more likely.