Did you test the final fight at all? it is borderline impossible as by the time you reach the final bounce the projectile is going so fast if you do not hit the parry it at earliest possible point the projectile will hit you mid parry animation.
Apologies I downloaded the game and have found that these issues are only present in the browser version. beat him first time in the downloaded version hitless (because i smashed my head into the browser version for about an hour).
DO NOT PLAY THE BROWSER VERSION IT DOESN'T WORK PROPERLYPatched now