My intent was to allow the player to stockpile up to nine potions. Here's what I did:
1. Changed the name of potions to Life Tank (1), Life Tank (2), ... Life Tank (9).
2. Made each Life Tank into a Potion type item, with level corresponding its name.
3. Other attributes were identical to original potions. (Not an equipment item, fills all hearts and magic, keep lower, etc).
What happened? Well, you can pick up potions, but no level of potion appears in your inventory.
So I went back and clicked the "equipment item" box. Now the potion will appear in your inventory, but it doesn't "level-down" when you use it.
Hooray custom item bugs!