Ring of Pain

You'll need to play through the game until you pass level 15. This will require learning the game and learning it well enough to survive till the boss level (which am I not going to go into depth on how to do here). Basic strategy for reaching this far is to grab as many items and stat boosts as you can, look for items that synergize well, for instance, pick up lots of freeze items or petrify items.

Once you pass level 15