Stunning game both visually and audibly! Really really impressive for the time constraint :D

Like a couple others mentioned, it would be nice to be able to restart from the keyboard (probably the space bar to match the start)

I would also really like to see some sort of combo, or at least making your punches cancel the enemy attack (could even be a weak and strong attack system where strong attacks cancel enemy ones but weak jabs don't), I think that would add a lot of depth to the game.

Another way to add a bit of depth could be to replace the 3 heart system with a heath bar to match the enemy's, which enables you to make each attack from the enemy have different weights to them, for example a leg sweep wouldn't hurt as much as a ground slam, so it would feel more rewarding to the player if they block a big hit and avoid taking a lot of damage.

There are really endless directions you can take this game! It's a really good base to build a larger project around! I look forward to seeing where you take this :)

Looks great! Given the difficulty it would be nice if the restart wasn't so many steps (using mouse to exit, then space to start again, all with the delays from the transitions).