Here’s an easy way to level up your sub-weapons. When you get to the Nest of Evil, head to the southern most locale of the area. You’ll find an enemy here called the Doppelganger. Head into the fight with nothing equipped (you must do this!), and then once inside where you fight him, re-equip your gear, including a sub-weapon. When he’s killed, he’s worth 99 sub-weapon points (that’s 198 points if you have the Master Ring equipped). This is a great way to level up your sub-weapons!