The Beast Eye is an item you receive from Gurranq, Beastman Clergy in Elden Ring, although what it actually does is not immediately apparent.
Reaching the Beastman Clergy isn’t easy, since most players reach the NPC after defeating the Tibia Mariner in the Summonwater Village through the nearby Sending Gate. Don’t panic, you didn’t get ripped off, and the Beast Eye is a useful item that can help you get more rewards from Gurranq.
The Beast Eye notifies you when a nearby boss drops Deathroot, which is what you can feed Gurranq for more valuable items. A message stating “The Beast Eye quivers” will appear each time you’re near a boss that drops the rare item, and you should always try to defeat them.
You can also summon D, the character that initially pointed you in the direction of the Sending Gate, at each boss that drops a Deathroot. Some of these bosses are difficult to beat at lower levels, so don’t feel ashamed to summon the much-needed health.
Each time you acquire a Deathroot, return to the Beastman Clergy for another prize. He will eventually become hostile, but he’ll return to a friendly state after you deal enough damage, and you can continue bringing him Deathroot.
This is an optional side quest, but the Beast Eye makes it easy to know when you can get a Deathroot, and the items given by the Gurranq can help almost every type of build. Just keep an eye out for the Beast Eye message at the bottom of the screen.