A bug that I've run into a couple times:
Getting caught by an enemy while in a checkpoint (whether chess piece or level entrance) will cause you to respawn with negative health and spirit if you die.
Also a couple bosses are very damage-spongey, necessitating getting every attack upgrade for it to not feel tedious to beat.
Otherwise, I'm loving this game, it feels like it just keeps going and going, revealing new content when I thought I was approaching a finish point. For a 0.3 alpha there's so much good content in here.