Seems like you may not be able to beat the final boss on Retro mode if you use a Continue. Which is how the Arcade worked iirc, but it'd be nice if they'd told you...

Even if I use a continue throughout the game and defeat the boss on the first shot?
Because to me it seems completely bugged and I have tried it twice. When the boss is supposed to die I get damaged in its place and the boss stops firing. And this pisses me off to no end.

No clue. Good luck everyone...