Press DOWN and PAUSE. Then release DOWN, but still keep PAUSE pressed. Now press RIGHT, RIGHT, RIGHT, LEFT, LEFT, LEFT, RIGHT, RIGHT, LEFT, LEFT, RIGHT, AND LEFT. You should now have access to all spells and levels.
QUICKGROW---leaf, feather, silver ring
SPIRIT BOMB---feather, gold ring, leaf
LIGHTNING---two diamond rings, feather
DUST DEVIL--leaf, silver ring, feather
DEMON------gold ring, mirror, necklace
SHRINK--------mirror, necklace, amulet
GHOST---------skull, tooth, magic root
PLATFORM---feather, tiger eye, feather