Castle of Elite - Official game guide|
Introduction - Basics - Solutions - Secrets - Trivia
The four secret levels
These are obtained by beating all the levels in a difficulty set. The first secret level, Jumpman, is based on the Donkey Kong arcade game. The second secret level, Mountain Climber, is based on the NES Ice Climber. The third level, Ancient palace, is based on NES Zelda II: Adventure of Link. The fourth level, Temple in the sky, is based on NES Kid Icarus.
In the fourth secret level, Temple in the sky, right-click to destroy one of the top-right blocks, which is literally sitting out of place. Go through the hole to enter the only sidescrolling level in the game, which references various parts from Kid Icarus.
Beat all the levels, except the secret ones, to get a different ending after completing Final Destination. All the outfits will be displayed here as well.
It's not much of a secret, considering it's written in the help file, is it? Press F5 to switch to the original cursor I created for the game.