The backgrounds can get really complicated, and they're just as important as any other part of the skin. Therefore I think they should have their own thread on the forum. If we can contrate the subject of background skins here, it will make it much easier to get help, and we'll put the pressure of some of the other threads. The simplest background is probably the one found in SMB itself. Apart from a few background objects, that are actually found in the Map sheet in SMBC, it's just a single color across the whole level. It gets more advanced with, for instance, Castlevania 2, where it is much more elaborate. Here's a example from my skin: The forest is the simplest. It simply loops. However, in other parts of the game, many more different background objects are scattered around much more frequently than in SMB. Backgrounds are animateable. This is from silentshadowxp's Legend of Zelda skin, and the fire is supposed to animate like in the small caves where you find vendors and such. The most advanced background in the game so far is probably the SNES Super Mario Bros. In addition to normal background objects, it also has a parallax background. Parallax is a technique where, as the camera moves, objects in the background move as well, but slower as to simulate depth, that they're far in the distance. There are many different parallax backgrounds in that skin, some of them even animated as well. I'll have to admit I have no idea what the requirements and restrictions for backgrounds are. My guess is that if the developers thinks your skin is cool enough, they'll find a way to put it in, background and everything.