I'm araid there's only the secret boss, as far as alternate endings go.
Cool! Does the secret boss refer to whats inside the walnut or something else? More playthroughs will ensue, also I've been showing this game to my peeps and they dig it too. Freak on man!
PS: the King fight is exploitable due to his projectiles not reaching to the back wall. The hand will come down 1 or 2 times but nothing else reaches in that spot. I don't know if these games get updated or not but let me know if you'd like the comment removed :)