Gazing through the shard of reflective glass, the world looks more colorful somehow. More alive. You are struck by an overwhelming feeling that there is more to reality than you yet know. - Eye of Ulos (RPA-ADV4)

A broken part of a mirror from Mikto, Plane of Secrets, that reflects the connections objects have with one another.

Picked up outside Taron's Arena.

When looking through the shard of reflective glass at the barracks of Taron's Arena, it is evident that Minthrok and Shortep have a special bond with their animals;

Looking around Minthrok’s shop through the reflective shard, everything takes on a special glow. Minthrok and Shortep appear connected to their beasts by silvery threads that emanate from their hearts. - Eye of Ulos (RPA-ADV4)

It is identified by Minthrok as an interplanar object, and shows many interesting things;

Looks like a shard of mirror from Mikto.“ - Minthrok

With the shard of reflective glass, you are able to see the bodies of the fallen palace guards in a new light. Their spirits rise intact from the pool of their remains. You hope they find a peace in the next life that they could not find in this one. - Eye of Ulos (RPA-ADV4)

Depending on when you inspect the scene at Taron's Arena, you find the glass shard in a head of cabbage or Zalic's uniform.