Using largely flixel's particle effect to achieve a stylish presentation, this feels like a complete game even without any bgm, minimalist to the finest, well done!

The most fun part is also the most annoying part, the jabbing. When you're hitting the mark in a streak, it feels so fun, on the other hand when you're just dancing silly trying to hit something, it's so frustrating.
But that's the point. It would be easier had you just use a 2 or even 1 button scheme, but that'd ruin the game. Nothing's more exciting when you're facing multiple enemies with this control.

As Gairse has already mentioned, I too suggest a health refill before the boss fight.
Not necessarily full health; making sure the player have at least 2 life would do,
(or just let the player roll back to try a better run)
because whether you can take 1 or no hit at all makes so much difference here.
I had only 1 life left the first time i reach there, and frankly, it's pretty much unplayable.

Other than that I had much fun playing. The boss fight was harsh, but not entirely impossible, and once you beat it it feels very rewarding.

SUCH a good game. The controls are finicky for a reason, guys. Don't blame the game when you can't do it.

The sound was amazing. Without music, the sound effects are like a punch in the face, in a good way.

Just the right amount of time was given between showing the enemy and the next attack for you to plan what you're going to do and it gives you a real feeling of satisfaction when you get it right.

I can only suggest a full health restore before the boss? It would make the fight slightly more forgiving, but I can see that's not what you were going for with this game!

while Holding z press the arrows to Attack

I loved the aesthetic, but the control are needlessly complicated. Map movement to A/D, and have the up/down keys automatically jab upwards/downwards in the the direction that the player is facing. Also, it is unclear when an enemy is about to spawn. You see the enemy for a moment before they appear, but it is easy to strike too early or too late, as there is no clear indication that their invulnerability has worn off. With these small improvements, you'll have a much, much less frustrating game.

The game has potential, but as it is is WAY too hard. And please, don't say it's "old style difficult" , "Nintendo hard" or some BS like that: most of the time is just plain unfair.
The sound design is OK, I guess. It would benefit from having some music.
Polish here and there (pause and restart buttons are much needed features) and you'll have a top quality game.