Quick question about usage rights etc?

[E-Man]

That mostly depends on if your game is for fun or for profit. If it's for fun, then you're mostly allowed to use the sprites to your heart's content (but there might be exceptions where you have to ask the original ripper or creator for the use of the sprite sheet). If it's for profit, however, that's a little more complicated. Besides having to ask the original ripper/creator abotu that, there's also the matter of practically all of these sprites are based on copyrighted content. I don't know how it exactly works, but you're better off commissioning someone to make you assets from scratch (unless you got permission form the game's original creators/company that owns the IP).