Besides the SH3 references the movie is based on there are more Silent Hill game hints. When the lead female is going through the names she has already used, one is Mary. That is the name of the woman you're looking for in SH2. At the end the truck driver Travis Grady is a character you play as in SH: Origins, and the prison bus that goes into the town and fades is a reference to "Silent Hill: Downpour" which begins with a prison bus containing the lead character crashing on the outskirts of town. See more...
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Plot hole: There is a scene where Heather pulls the mask off one of the cult-members, and the air literally poisons him, causing his skin to discolor and his throat to choke up. This never happens before or after. Vincent claims that those particular cult-members have superstitions about the air being poisonous, but there are a multitude of problems with this explanation: A) We have seen numerous other people go unaffected by the air, and B) we later see several of these same cult-members in the sanctuary, unmasked, breathing the same "poisonous" air with no adverse effects. (And Claudia had stated that even the sanctuary is no longer safe from the darkness of Silent Hill, so they are technically breathing the same "poison" air that's outside).