The rare elf "Zero" is found in Forest Of Dysis (the stage with the forest) when in easy mode. Once you are in the inside part of the stage where you fight the statue that raises water and throws purple beams, destroy the statue. Afterwards, jump the pit and slide on the left side wall through a secret passage. Keep sliding down and on the way you should find the rare elf. If you keep sliding down, you will reach a secret area with lots of crystals and an extra life.