The rewritten Style Guide has an open discussion of the spoiler policy. The current policy will be used if no new consensus is reached. Discuss it here.
Uh ok you need to chainsaw either the Mysterious Maid, Desu-Chan, and/or Onee-Chan, then go in an out of the bathroom a couple times to clear switch #0001. After that, just walk towards the stall and the monster will pop out. Being invisible bypasses it.