Ok, so I think I broke your game multiple times, but thanks to that, I was able to kill the harpy, even though I didn't get the victory screen.
When I first saw the harpy, I took a screenshot, and by the time I was back to the game, the harpy was nowhere.
I thought I fell back near the bottom so I started to build up my pair of boxes again, until I found the top of the map, and eventually escaped left everything below me.
So after I got bored I decided to take a leap of faith. Fell so fast my character left the camera behind way past terminal velocity, and half way through I saw a harpy-like blob before the camera could catch up with me. So started to build my way up again, and then I saw the dead harpy, under a huge pile of blocks. It was a wild ride, I really enjoyed it, not gonna lie. :D