Part of a commission for fionagrace on FA - thank you!
It's just Bullet Bill. A tiny sprite, but a classic enemy. This style is from Super Mario World on the SNES. He's done up as a magnet in this case.
This sprite is an example of one that is small enough that you want to look at it from a distance. Up close it's sorta ehh, but it looks great from a distance. It's really the type of thing that make a perfect fridge magnet, which I imagine this will become.
Original sprite can be found here: http://www.spriters-resource.com/snes/smarioworld/sheet/52779/. Credit goes to Tonberry2k for the rip.