An 2012 Free RPG Day adventure for Dungeons and Dragons 4th edition by Wizards of the coast.
From the back of the book:
Show this Beholder who's Boss
The Keepers of the Celestian Order, valiant defenders dedicated to destroying horrors from the Far Realm, have trapped a beholder in its lair. However, the evil aberration has proven far more dangerous than expected, and the Keepers need the help of adventurers to end the threat of Omaranthax once and for all.
This Dungeons & Dragons Roleplaying Game adventure, created for Free RPG Day 2012, pits player characters against a mutated beholder and its vile underlings. Although set in the Forgotten Realms campaign setting, the adventure can be easily adapted to any D&D world.