Behold the Watcher is the first boss encountered in Magicka.
After the players fall through the hole during the party, they will have to make their way back up. At the end, their way is blocked by Behold. Although he doesn't attack the players, a health bar appears, signalling the players to kill him. After killing him and going back upstairs, Shams will inform the players that he sent down Behold to find them, but it is unknown to him that the players killed him.