No one can harm you by using grafics from a comercial game into your free game. The only thing they can do is send a e-mail asking you to stop the distribution, and this will only happen if your game makes more sucess than Minecraft...
So, don't waste your time and be happy: http://spriters-resource.com/
If you want to be sure about that, just search for Mario and Zelda fan games and you will find tons of it that use their grafics.
Huge companies like Nintendo doesn't waste their time running against fan games, i think they even like it because fan games only make fans more fans XD
I have a RPG Maker game that use "Tales of" series grafics, and nothing happened.
If you want to see it:
Ah, and remember to say that you does not own the grafics and give credit.