Open two player mode and look at the lifebars on the left side of the screen - blue for first player and red for second player.
Now when you look at it on different emulator, these lifebars are represented differently.
When you open this game on puNES: both lifebars are blinking/flickering constantly.
When you open this game on Nestopia: there are slow blinks/flickers for first player lifebar (blue) and nearly no blinks for second players life bar (red).
When you open this game on FCEUX: there are no blinks of life bar that I can see.
It would be good to check on Nintendulator but I dont use it.
Which one is correct? Only one can be right
This game was released under different titles (no matter what region you use - it hapens on each of these):
Japan - Kage
USA - Shadow of the Ninja
Europe - Blue Shadow
Edit: Videos on the real NES (thanks to FHorse for finding them). But it can be misleading due to poor quality:
http://nicoviewer.net/sm12506237
http://nicoviewer.net/sm12525619