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By Anonymous
"To unlock the door you must defeat all High Thespian's in the mansion in the order they appear on the door (from left to right)."

This would have to be one of the stupidest things I can remember a game implementing. Well done to anyone who happened to kill them in the correct order the first time they came through this area.
By Anonymous
neoseeker has a guide as to how to do this, making it worthwhile, the reward is the Archon Greatsword.