Alphakill

I heard RSX has a feature normally unsupported by PC gpus called Alphakill. What it does and how do you emulate it also does RSX has any other atypical exotic functions or fixed function hardware that is hard to emulate like this like for example Gamecube's Zfreeze.

One of the weirdest things that I encountered was Destiny trying to access gl_Position in a fragment shader!
vlj probably knows a lot of weird things about RSX.