Upon entering the dark room, you hear a loud, chilling sound. A light flickers to life and illuminates a relatively small room. It would be a relatively pleasant place to take a nice long rest, but unfortunately it seems to be filled with several beholders. The entrance, which conveniently doubles as the only exit, slams shut behind you. your party frantically attempts to ready their weapons as the panic begins flowing over you.
"WAIT!", cries your resident creature expert. "Something's not right here. Beholders hate each other. There's no way that there would be more than one in this little room."
"Then what are these?" another party member asks.
After a bit of thinking, the creature expert responds, "it would seems these might be gas spores. They imitate beholders and explode from the tiniest injury. We definitely do not want that happening in this cramped space."
After some extended discussion, your party decides that something had to cause the sound and trap you in here, meaning one of these is a real beholder.
"Brilliant deduction, adventurers", comes a voice inside your head. "I am a disciple of the great Gzemnid, and I offer you this challenge. If you can find me, I will spare your lives, but if you choose incorrectly, these imitations will explode and kill you all. I'd wish you good luck, but I rather enjoy when the heroes go boom."
You look to your companions and determine that either they can hear the voices in your head, or they also got the message. You split up and carefully examine all the creatures before regrouping.
It is up to you now. Find the beholder.