Easy "Untouched" trophy
Note: This only works with one of the main eight bosses, in the "Lair of ??? Knight" levels. Choose any Boss and attack them while using the Phase Locket repeatedly to remain invincible. With a fully upgraded magic bar, you will have plenty of magic remaining. Consider using this on King Knight. He has poor defense and does not have many invincibility frames. If you get hit, intentionally die and restart the fight from the checkpoint.