If the experts are correct then there are only two Primal Rage 2 arcade boards in existence, giving it a near legendary status. Now there's one sitting in the Galloping Ghost Arcade ruining all that elusive mystique.
Galloping Ghost's Doc Mack says below that this is an original 0.36 prototype and potentially one of only two in existence (the other being owned by the game's creator). Despite being almost irreplaceable it's now been boxed up in a cabinet and put out for all to play (thanks Joystiq).
Here's the original video of gameplay when the board was discovered in 2012:
And some gameplay streamed by the Galloping Ghost: