I don't get why everyone is complaining about the cooldown when all mobs and players had and still have a point of time in which they're invincible (or, to put it another way, it's a delay. Find an animal or something and keep hitting it to see. The invincibility lasts as long as the cooldown)...
That "invincibility" is not invincibility at all lol. It's the natural tick delay that comes with anything in Minecraft and it lasts no where even remotely close to as long as the delay added in 1.9.
