Click to enlarge. Artwork is currently only from the Japanese manual. The art has not been cleaned in any way, so expect chunks of page borders and text.
There are unused tiles that would have given Kahs's eyeball a bow. I have no idea why.
A cute croc is in the Area 2 tileset but sees no use.
This unused rolling thing (a tumbleweed?) is stored with the Area 5 enemies and has all necessary animation, but is totally absent from the game.
Mogurun was apparently meant to burrow underground, but he does no such thing in-game.
This leaf and swirly thing are found among Area 7's enemy sprites.
Perhaps most curiously of all, the World 8 tileset (seen only in the final battle and Battle Mode stage 6) has a unique door, button and raising pillars among its graphics. It's likely World 8 was planned to host more than just a boss rush.