Heading down the rabbit hole…
Qwikiverse maps the references between stories: what Batman: Arkham Asylum nods to, and what nods back. How it works
May be found at the following website: http://i23.photobucket.com/albums/b376/WOXOVOXOW/1401204244.jpg.
Fair use
Nothing spotted here yet.
A line quoted, a cameo, a character named after something: if Batman: Arkham Asylum nods to another story, or another story nods to it, spot the first one.