RetroN 5 Experiment - Four Player NES Games

While working on another video, Sean thought he'd try out something on the Retron 5 that didn't occur to him when we did our Keep or Heap review; controller adapters like the NES Satellite and NES Four Score probably don't work with the Retron (and can't even be plugged in unmodified), but one of the console's built-in features SHOULD make that unnecessary. But is he right?