That was awesome! Way more addictive to play than I was expecting at first. I love the artwork of the enemies and of the player tower. The lightning and fireball attacks were also very refreshing from the normal attack. I definitely think that the one thing I want the most to be added is a donate all blood button. And it would also be awesome to see what stats get increased (x% -> y%) when you get blood upgrades.
I really love the different tiers of upgrades too and their different icons. Personally I never felt like it was worth it to upgrade health? I think if the enemies had appeared in waves that might make health + regen a lot more useful as I seem to be overrun as soon as an enemy hits my tower.
Just a bit of music or SFX for hitting enemies/picking upgrades would be sick too in the future :)
I would totally love to see any other upgrades/attacks/features added in the future and I think you could do a lot gameplay wise with the game.
Really fun to play and thanks for submitting it to the jam :D I think you did a great job with this game