When certain Neogeo Pocket COLOR games are inserted into a non-color Neogeo Pocket system, developers sometimes included secret error message screens.
SNK Vs. Capcom: The Match of the Millennium takes it a step further by not only including several error screens, but one in particular gives the player hidden instructions on how to view a secret ending viewer when playing the game on a Color system – put the game in a B&W system, then put in a Color system and win the Tourny mode, then press OPTION on the title screen. (Fast forward to the 5 minute, 19 second mark for more.)
