Tutorial below. Pure gameplay in the video.
I saw many comments asking how to beat the boss on the scratch page, here is a very basic tutorial video on how to beat it.
How to avoid and counter different attacks
Charge Attack
Wait for him to charge. Jump and land on his head while he is running. This is known as a stun, freezing the boss for a few seconds. Take this time to whack him from behind until he slams the ground, as shown. He might seem intimidating, but he is most vulnerable in this attack mode.
Crossbow Attack
Repeatedly dodge between the arrows fired. Try to dodge between those with a larger gap. If you're feeling brave, you can rush towards him attack.
Strike Attack
Just jump over his head until he switches to Charge Attack or Crossbow Attack. He is pretty much invulnerable in this state.
0.11 - Battle Begin
0.16 - Charge Attack
0.30 - Crossbow Attack
0.37 - Strike Attack
0.40 - Battle
1.41 - Victory Animation