This tileset gives you all of the important stuff as far as tiles from Super Mario Brothers (NES). Furthermore, it adds some recolors that allow you to make stages in ways that weren't possible before. For instance, you can have an underwater fourth stage, or neat bushes inside of an underground stage to make it seem like a natural cave. Included here below the resource are two screenshots showing off what you can accomplish. Please let me know if I missed anything or if you'd like something added, and enjoy the tileset! (No credit required.)

Neat recolors. This could allow for some really different levels.

How is there fire under water

Who puts fire in water

Why would someone swim through water with fire in it?

1. I think it's lava, not fire.
2. It's better with hot water than with cold

Uh, everyone knows Bowser spits out fire, not lava.

Who said that was bowser?

Roph.

Yes, it is bowser, underwater, with a snorkle.
Fire is underwater because it's a dungeon stoopit.

Actually the mario games have done that several times before, it's nothing new.