ok. I have updated the page and added this in the page to help kind of guide you, but I will also write it here.
Movement:
A/← (left) D/→(Right) Spacebar (Jump) Left Mouse Button/Left Click (Attack)
Tips for fighting boss:
- hit the boss as much as you can
- hit/attack the dice shards to destroy
- attacking is in front of you in the direction you face.