This is best done when you unlocked all the equipment, but if you just finished the game and don't care looking for all the weapons, armour and shields, just start another game in Easy or Normal and in the main menu use
to input this password:
MJWH WC5 TY3B XJR
You'll be at the end of the game with all itens. Just equip the Tasmanian Sword because it have the ability to let you change between characters if you jump, press
and
. After that just follow this video to the location of the Charm Stone.
Obs: video is not mine, so feel free to thank the uploader for it