The boss is a larger version of the Monstars, with horns on its head and clothed in royal seeming clothing. The boss is initially sleeping until Tim walks close enough to it. Then the boss will begin walking around, spewing out 5 fireballs in a row at the player every few seconds. In order to defeat him, the player must drop chandeliers onto its head a certain amount of times (usually 5). However, there are only two chandeliers to be dropped (unless playing a mappack). Upon defeating the boss, he will die, become decoration, and drop a key.
The boss's clothing may suggest that this is what Tim sees the Knight as, and what Tim wants to do to him.