Nice work! This is a good, solid base for a roguelite platformer.
The theme is kinda generic at the moment. It needs a gameplay gimmick, a novel aesthetic, and an emotional core in order to really suck the player in. The sooner you add those, the better, because they're the kind of thing you want as your pillars of game development. Once you figure them out, they should inform all of your creative decisions.
Gameplay suggestions ranked in order from most to least important:
> My Xbox controller is a little old, and the thumbsticks tend to rattle a little bit when I let go of a direction. Make sure you have "dead zone" in the middle of the thumbstick. (I.E. the character won't switch direction unless absolute value of the input > 0.2 or so.)
>I'm pretty sure you are using "Coyote Time" for jumps, because I didn't feel like I was constantly falling off of ledges when I jumped, but the bottoms of walls need an equivalent of Coyote Time but for for wall-climbing. It was WAY too hard to catch the bottoms of some floating islands and start a climb.
>I'm unsure if the above is the reason why, but I had trouble climbing walls sometimes. It feels less responsive/intuitive than Megaman X. That's a benchmark you should seriously be aiming for. Less involuntary X movement when jumping off of a wall or more rapid change from the automatic movement to the player's input would fix the problem.
>At the bottom of the dungeon, the GUI sometimes covers up enemies at the bottom of the level. Just add a layer or two of solid dirt to the bottom at level generation to fix this.
> Give the player feedback when the player character takes a hit, even if it's just them turning white for a frame and playing a sound effect. (Needs to be different from the sound when the player hits an enemy because we're never not hearing that sound.)
>I dislike how the gold disappears behind slime, weeds, etc. You should render the gold on top, just like you would enemies, because the gold is a functional gameplay mechanic! GUI > Enemy projectiles > Enemies > Player > Collectibles > NPCs > Chests/Boxes/Pots > Interactive objects (lifts, moving platforms, buttons, etc.) > Dynamic decorations (blood spatter, debris, etc) > Collidable walls/floors > Static decorations (furniture, statues, etc.) > Background walls > Distant Parallax backgrounds
> Likewise, a sound effect when you pick up gold would make collecting gold feel more fun. Juice it or lose it!
> Whirlwind attack, while kinda fun to pull off, is no better than using your basic attack, because the enemies get knocked back, so you need to drain your entire magic bar just to kill one enemy who you could easily stab three times instead. (Maybe this could have a place in future versions if there's dozens of mobs swarming you in a room? But in the first dungeon, it's useless.)
Yes, these suggestions are "polish," but they're polish that affects the core gameplay. Remember, Miyamoto spent ages perfecting Mario's jump before doing anything else! You should, too.
Good luck! :)