It's a good thing the early Mario games were so low-fi. If they'd shown your enemies in as high a resolution as they appear here, we'd have all been crapping our childhood pants.
These, uh, interpretations of some of Mario's foes were drawn by Mike Puncekar. Some of them, like Lakitu, are just cool. But those Boos would have been a little much for my under-developed sanity to bear.
You can see more of Mike's awesome art below.
Mario Enemies [Mike Puncekar]