The Cursed: Gloomfrost Reflection

[Part of the Cursed story line]

The Gloomfrost happens to be the top of a really tall mountain and after the team deal with some polar bears, frost salamanders and yetis use hastened invisibility once more to reach the cave at the summit. This cave is mainly home to remorhaz and ice golems - none of which see the party run past.

Upon finding the seer and requesting for help, she simply gives them a plain mirror and tells them to show it to Wyldfene. Marchon is a bit pissed at this ("we traveled all this way for a mirror!?"), but fortunately the seer also teleports them back down the mountain afterwards.

Maybe it's one of these future tech mirrors?

As instructed, the six adventurers then return to the barbarian camp and are once more granted an audience with King Wyldfene, who is more interested in just executing them on the spot this time. However when shown his own reflection, the spirit dragon inhabiting Wyldfene goes berserk and flees - leaving the corpse of the barbarian leader to collapse in a heap.

Insight: There are traps on the second level of the Gloomfrost, but triggering them won't break invisibility so you can just alternate leads to tank the damage.