Actually, I know it's not very clear but if you wait 2 seconds after a hit your next hit will do 1.5 times damage so if you line up all 4 to have the enemies chasing you then you can kill all of them in a single hit with that strategy. From my testing it's way more efficient to do it this way but it's not intuitive nor the easiest way and as such yes, you're right more tweaking is needed.
I think most importantly I should have made it more clear that's how you do a critical hit. Right now I just have a visual indicator of when it happens by having some particles swing out of the sword to make it look like you're swinging it through the air much faster. It also says it in the description on the games page but I doubt most people read that. Other than that the only way to tell is by looking at how much the enemy hp goes down.
Maybe this just isn't enough of an incentive to not just spam your sword. I want spamming to be able to still happen because when I made it so you were forced to take time between your hits it felt sluggish. Maybe I could do some sort of ramping damage so first time you wait 2 seconds it's 1.5x damage then next consecutive one it's 2x damage and keeps scaling till you do an attack too fast. There's a lot of different ways I could attack this issue. Thanks for bringing it up!