So, I was thinking
about Freddy and his power of fear. I did some research to see if The Joker has fears.
As the above link mentions, he has been proven to have fears, just cope with them by being insane, thereby neutralizing his fears. He finds them funny. So all he would do is laugh at Freddy till Freddy could no longer use his power of fear, drag him to the real world, and shoot him. (Most likely with a rocket, knowing his tendency to go overboard) There that is put to rest.