You should ask in the forums for said games. Or view the games guides.

Or look it up on the gaming wiki.

There is a trick to getting infinite lives in mega man. I don't remember how to do it, but i remember it was similiar to super mario game tricks.

Including cheats in games is a trend that's been basically dead for ages. Nowadays almost the only recourse is to use Cheat Engine or mod your game.

Which is a shame, it was its own kind of fun to IDDQD in Doom.