Hint: Creepy Call
Whenever you walk around in Henry's apartment, go to his bedroom and look out of his window. If you notice, you will see a billboard that says "Bar Ashfield" on it and right below it as a phone number. Then go to his phone next to his bed and dial: 555 – 3750. It will play a little creepy call makes Henry feel disturbed.

Hint: Moving Loading Screens
Whenever you enter a new room and get the loading screens with the weird symbols, move the left analog stick around and watch as they move across the screen.

Hint: Possessions
Throughout the latter part of the game, your apartment will become possessed and/or haunted. If you took the Shabby Doll that the mysterious man gave you inside of the Apartment World, Ghosts will slowly come into your apartment. No matter what, however, your apartment will become possessed from time to time. You must eliminate these possessions by lighting Holy Candles near the possessed item, or equipping a Saint Medallion once you go near it.