Only upgrades currently present in game are from level-up (blue bar under health bar)
Weapon auto-attack is based on enemies present within attack range. I agree that it’s not intuitive, but it was designed that way, since initially there was ranged weapon option planned.
Glad you liked sprites, it was my first real-ish experience with pixel art. As for background, it’s not perfect, but I prefer it over flat color. In ideal world, I would prefer to have some kind of objects laying here and there to visually anchor player’s position in arena.
And thanks for your review :D