Mega Man Anniversary Collection Cheats

Go to the weapon menu and select the Pharaoh Shot weapon. While holding the square button, leave the menu. The weapon will start charging up (you'll see a ball over your head), but will not use any energy.

Once it's fully charged, you can ram the ball into an enemy. The moment you hit an enemy with it, press Start. If timed correctly, the Pharaoh Shot's energy will not have decreased. You can now do this trick again if you want to.

You need the Flame Sword power before you do this
First find an area with a vampire bat and equip the Flame Sword. Let the bat dive at you and right when the bat latches onto you use the Flame Sword. If done correctly you should see a silhouette of megaman's head behind him and every time you move a “box” of silhouettes will appear in front of you. Every time something touches these silhouettes it damages them.
Note: This glitch is cancelled if you are hit or use the Flame Sword again.

In Mega Man 1, when using a weapon that goes through an enemy --- Rolling Cutter, Thunder Beam, Ice Slasher, or Fire Storm --- press Select the second the weapon hits an enemy. After you press Select again to unpause the game, the weapon will hit the enemy a second time. This makes a joke of virtually every robot master battle in the game, so long as you have a weapon that can be used in conjunction with the glitch.

Unfortunately, this was fixed in later versions of Mega Man, and does not work in any other title besides Mega Man 1.