I like to draw mockups for my favourite retrocomputer, Commodore Plus/4. Sometimes I get idea about a newer non-retro game, other times I draw pictures of other newer-but-retro games (mostly from SNES aka. Super Nintendo Entertainment System).
These picture were inspired by the famous Super Mario All Stars from the SNES.
This larger image contains the full map of World 1-1:
You can find the original map at http://vgmaps.com/Atlas/SuperNES/index.htm#SuperMarioAllStars.
The pictures contain only the backgrounds and other game elements except the player avatar and enemies. I don't like drawing enemies :)
Drawing the mockups I always try to keep in mind the hardware capabilities of the +4 machine (320x200 or 160x200 pixels, very restricted color capabilities, etc.) The final result is always displayable on the real iron (or in emulator) as a static image.