I need to play more of this. The art is amazing as always, the sounds when there are sounds fit the game well. I move way too slow when I'm not using the gem to the point where it feels like a literal crawl. If that's done on purpose, then of course great job, but for me it made it kind of frustrating, especially given the fact how fast you can die and how jank some of the hitboxes can feel.
The inventory system, although fun, I think needs to really separate usable items from materials. This might be a fun suggestion to experiment with:
Instead of using Q&E for swapping back & forth, have both keys scroll forward through 2 different rows of items, then whenever you press the button to the corresponding row, it will put that item in your usable slot. This way you can kind of create patterns of combos and items Final Fantasy Black Mage style! Idk just a suggestion hahaha