Here's the well know Devil Dragon from Mega Man 2 for use in SMW as a boss of some sort (or at least one that you have to run away from). Included with this download are two different versions. One is an 8-bit version from the NES Mega Man 2, while the other one is a 16-bit version seen in Mega Man: THe Wily Wars for the Sega Genesis. Credit isn't required if you use this, but it would be appreciated.
Note: If you want it to "chase" after your hack's protagonist, make the level you put it in a layer 2 level with layer 2 interaction, layer 2 scrolling set to none, and with an autoscroll sprite, then put the dragon on Layer 2.