From the Castle Greyskull wiki page :
"In the episode "Double Trouble", an evil doppelganger of He-Man's friend Kol Darr also comes across the chamber that houses the Secrets of Castle Grayskull. It is a room with two doors, between which sits the Guardian, one of which houses the secrets, the other one is the only destruction."
So, basically, you come into the room and are faced with the Guardian.
But this means, you either came in from Only Destruction, or you came from where the Secrets are kept.
If you came in from Only Destruction, you're probably not too worried about the Guardian.
And if you came from where the Secrets are, the Guardian is just there to warn you not to go into Only Destruction.
Seems a bit silly, either way.
#greyskull
#skeletor