Cool idea, but way too hard. I see the idea behind the attacks predicting your movement but at this point it is too punishing and it is really difficult to "outsmart" or "outdo" the enemy. If this is a boss fight, I think the balance might be alright.
I'd be interested in how you will utilize the mechanic towards your idea, where can this mechanic grow from Undertale.
Other than that, you can sometimes strike twice in the same spot by quickly waving the mouse over the same sparkle.