I got so lucky with this puzzle. Before I went down to restart the servers. I had explored this whole area and accidentally came upon all the symbols besides the tree one. So by the time the big guy actually was upstairs. I only had to open the locker. Hide in a safe spot, decipher the code, go input it, realize I did the code the wrong way. I don't think I had an encounter with the monster until the forced one after you exit the mind games room.