1. A spinning structure, seen during the final fight against Walter, is based on the gravity drive device from a 1997 sci-fi horror movie "Event Horizon".

2. Some of Silent Hill 4 cutscenes vary depending on Eileen's health.

3. While SH4 doesn't have a UFO ending, the Channeling Stone exists in the game's files along with other unused items and is accessible in the game with the help of cheating devices.

4. Jasper Gein looks very much like Daniel "Spud" Murphy from the 1996 film Trainspotting following the story of a group of drug addicts.

5. A Cecropia Moth can be found on the spiral staircase (between Subway World and Forest World revisited). Normally it is barely seen without using camhacks. This may me a nod to Alessa's hobby.

Alessa's room from SH3 with a moth collection:

6. The only SH4 weapon you can still fight with after it breaks is the Wine Bottle. It even becomes more dangerous as a weapon when broken.

7. The photo in the living room of room 302 depicts Venice, Punta della Dogana. Henry got this photo from Frank Sunderland.

8. Cynthia Velasquez looks strikingly similar to an American fashion model Alyssa Miller.

9. Jasper wears a T-shirt with an image of Incubus (SH1 final boss) and the word "Haures" beneath it which is another name for Flauros (an artifact featured in SH1 and SH0).

10. SH Downpour: Anne's Story contains a scene where Anne is dressed in Eileen's nurse costume from SH4. This comic also has other references to different SH games as you might've noticed.