Too much clicking! So many actions could be made faster with the introduction of tooltips.
Grinding for ingredients could feel like a crude solution for running out of potions, but the hearts drop once - that's a clever solution!
Felt very easy and exploit-like when I could just run to the first encounter to grind. Could only restrict the player to the last 4 or something - so the player doesn't progress unless they know they have enough resources.
Overall, I liked it though!

I had a fun time playing your time! I found myself going back and constantly farming resources to prepare for the last battle:

The three potion types were quite distinct (heal, single attack, multiple attack). Do you have other ideas you'd like to integrate in future builds?

I found the graphics in your game just amazing. The sprites and enemy design stood out, and the animation for both the attack enemies and throwing potions was fun to watch every time. One suggestion I had has to do with the hub, where you choose the battles and make potions. If it's possible to update the camera to show the next battle, I think that would help streamline the gameplay and prevent confusion early on. I found myself playing the second battle multiple times before realizing I had to scroll down to fight the next battle. Also, if it's possible to label each battle, I think it would be helpful. I had to frequently go back and fight specific battles to get more materials, such as bones (stage 5), and ghosts (the stage right before the final fight). Something as simple as numbering them would be good enough for me (I found myself counting up from the top to find the skull battle). 

I think the UI can be improved in a couple of ways. In battle, if the potions can be organized by potion types, that would be helpful. If it were organized similar to the way it's shown when brewing potions (healing on top, single attacks in the middle, and multiple attacks in the bottom), it'll be easier to navigate and choose potions during battle. I guess one challenge would be if the player doesn't have certain potions made...? I still think dedicated "shelves" would be handy to the player.

In future builds, if you're able to integrate tooltips, I think that should also streamline your game as well. Being able to just hoover over the potions I'm interested in to verify damage dealt, and then click on it and then click to throw would streamline battles, and eliminate the need for the "throw or cancel" pop-up. However, if you do play to make this a mobile game, I think your current UI flow is fine in this case.

Overall, I had a great time playing this game. A lot of my suggestions above is a matter of streamlining certain aspects of the game, and definitely didn't ruin the experience for me. Awesome job on this one!