Hey! I gave it a try, and here's my feedback
* How does the combat and movement feel? Is it fun to control?
It's definitely fun! With the fireball upgrades and the vampirism I could steamroll the first 20 floors — it was like being the final boss of a bullet hell game, and it was really entertaining. Depending on the level of difficulty you want to add to the levels, you may want to make the level caps higher or give the upgrades every two or three levels instead of every level, because within a few minutes of gameplay I felt like I was already breaking the game lol
* Is the Tavern hub actually fun? Does brewing potions and upgrading your character feel rewarding?
i was looking forward to try the tavern hub, but it feels a bit too simple on the aesthetic side. When I think of cozy potion brewing games, my first thought is Potion Craft, which is primarily focused on that gameplay side. At first I couldn't understand if I actually lost the minigame, because there is no reward indicator that the potion is done. It could definitely be improved with graphics and sound effects to make the experience more satisfying. Upgrading the character, on the other hand, feels like I'll have even less difficulty beating the levels, which links with my comment above.
* How is the difficulty?
It's low, but playing is still fun, specially given that cozy games don't require a high amount of skill to be played.
* Did you run into any weird bugs?
Not a bug per se, but many screens were still in German, specially the one with the relics, which makes it hard to choose one when I don't understand the "high risk high reward" presented. There was a moment in which the gold coins were spawned outside the dungeon, which made them impossible to reach. Also, I figure this is part of the rogue-like mechanics, but I usually came across chests that couldn't be opened even after clearing the level, and as far as I'm concerned the mobs were the one who dropped the keys.
I hope my comments are useful! Looking forward to the next builds (⌒▽⌒)☆