You are spawned inside the realm by Oryx as food for his minions. After you kill all of the realm's quest monsters, Oryx feels threatened and seals off entry to his Realm. You have 2 minutes to breathe and kill your last foes before you must enter his castle and defeat the minions that lie inside. Once completed you must face your own doom and challenge Oryx in his chamber to free the Realm!
Source: RealmEye Wiki.
Oryx is the evil antagonist and ultimate boss in Realm of the Mad God.
The godly creator of the whole realm, Oryx intends that players will become food for his minions. He issues taunts at the players as they progress through his realm and will shout his displeasure if any of his event bosses are destroyed. When enough of his servants have been defeated, Oryx transports any remaining players to his castle, where he lies in wait to battle them in his chamber.
If vanquished, Oryx retreats to his Wine Cellar stronghold where he fortifies himself in order to confront any galactic serfs foolish enough to pursue him there.