The first Mega Man game (like hundreds of other games) has a 'feature' where if you get hit, your character flashes for a few seconds and is invulnerable. And in Mega Man, this also extends to the boss characters. Probably to keep you from trapping them in a corner and getting a cheap victory.

But you can totally get a cheap victory anyway.

If you hit a Robot Master with a shot of any weapon you like, he'll start to flash

But if you hit Select to pause the game and wait a few seconds

You'll find that the momentary invulnerability he enjoys will wear off while the game is frozen.

Allowing you to unload a stream of shots, and as long as you pause between each one, they're all going to hit home.

Making it much easier to win.

The arcade Mega Man games are just like the console versions, just distilled down to the boss fights.

And, also like the console games, each of the Robot Masters has a weakness to one of the weapons of the other Robot Masters. It's kind of like a game of Rock, Paper, Scissors, only with six choices.

But how do you know who's weak to what?

Easy! Just try everything you have in your arsenal, and if you hit on the weak spot, the screen will flash white.

Which is kind of hard to show here, since this site has a white background, but trust me, you'll notice it.

And it's way easier to see than trying to check out the power meter at the bottom of the screen during a heated battle.