I know this is an old topic but I thought I share this.

https://www.youtube.com/watch?v=Knqpi6h9CC0

Is this by any chance could be the rumored Mario 20? I heard rumors of it before too and just today I bumped into the rom.
This is not Rockman 5 though, it is a hack of Mega Man 5. The title screen is not even changed in it so I am not sure what to call it. The rom I found is just called MegaMario but the rom not even properly named so it could be just a randomly given name. Lucky enough I could find a video of it but it does not shows the changed intro.
Honestly I can't tell if this is a fan hack or a pirate hack. But this seems to be the closest thing to the rumored Mario 20.