A growing sword and a combo meter are both fun takes - both jam theme-wise and as game mechanics! I liked that as the combo meter went up, I actually became more cautious as I got more to lose.
This could be improved with some 2D physics: my best strategy was to hide inside the boss himself and keep hitting until it was time to dodge. It was also hard to understand the hitboxes and if the hit has connected - I expected some kind of sound feedback from it. I also had a funny lockup at first when the MC got completely hidden behind the boss and I kept pressing arrows instead of WASD so I thought the game was stuck :)