I thought this was one of the better interviews, and there has been a lot lately.
Q: Regarding Jason's mental capacity, is he just horribly deformed? Or is he, as Ginny posited in Friday the 13th Part 2, "a frightened retard"?
Derek Mears ("Jason"): I think there's a mild retardation, but he's a smart guy -- he sets people up [in the film]. I think it would be more of a deformity with a mild retardation. Even though Jason does kill people, the filmmakers wanted to lend him an air of humanity -- something with which the audience could empathize. You know, he wears the mask to hide his pain and all that. That's a symbol of -- "That's my protection from society". I don't know what the writers intended, but that's what was going on in my head.Damian Shannon (co-writer): He's a sympathetic character. We understand his backstory -- he was neglected, he was ostracized, he was different. He was neglected and supposedly drowned, and then they cut off his mother's head. That would make anyone very angry, so we understand his reasons for killing.
And a bonus treat, Ryan Rotten's spoiler free review of the movie.