I found (early on, at least) an easy way to aim for a tank that just shot at you is to point your cursor at its front. Puts your paddle in just the right spot to bounce the projectile into their path.
So on floor 99, I buy a mighty sword from the shopkeeper, and then on floor 100, I use aforementioned sword to beat his head in?
He does not seem very bright, me thinks
 "Shield Defense"){kind=icon}
 "Get Off My Lawn"){kind=icon}
 "Elements of Arkandia"){kind=icon}
 "Soviet Rocket Giraffe Go Go Go!"){kind=icon}
 "The Enchanted Cave"){kind=icon}