Now that they're colored I think it's a bit easier to tell.
For games that have really low-res graphics, I think your going to need to build one heck of a manual. People generally read the manual especially when it comes to old style games like this. Simply put a picture of the creature, the name, and a short description and hints on how to defeat it.

You may get better responses here: http://www.byond.com/members/PixelArt

Although, the forums seem very...slow last time I checked.