Dear Blender Team
I was afraid my short description would not sound very sophisticated, so I created this little pitch, featuring a few quick examples you can do with the light path node.
No compositing was used in any of the images
Suzanne does have a brain after all.
Additive Particles in Cycles
With a special looking glass you can see that - at least toy - vampires do appear in Mirrors, but they are inverted, so to the naked eye they cancel out their reflection...