The Brotherhood has a room next to the entrance. When you play with Mei and Corey, go there, there will be no monsters there, but there will be a taser in the box (3rd key in the dressing table next to the door).
When we save YUN, if we quickly ran to the monster that grabbed her, and we run right up to him, he throws YUN, she runs into the basement. We kill the monster, run to the lobby, look at the monitor, set it up and escort the hero who is currently activated through the basement to the electrical panel and open the door to the basement. We go down to the basement and look for YUN….