coincidence

[MassacrMan]

I think you are all ignoring the biggest proof in that they both have 'dark' in the title. I mean, that's undeniably plagiarism right there. It's quite literally (Woah! My brain can't comprehend how fitting that word is) written proof! They didn't even try to cover it up. They could have at least changed it to 'dimly lit' or 'curiously absent of light', I mean, come on!

Amnesia: The Dimly Lit and Curiously Absent of Light Descent.