Super knife speed hack?

How is everyone having this hack...? they literally have a knife that is super ultra speedy..I know there are hacks that you could buy,But when I asked someone in ZM(crater) where did he get that from? and is it free?He said its Not a hack,But its a "code",and its free. the guy literally killed the boss in less than 2 seconds after hitting it..

HALP

He is referring to this hack
https://www.youtube.com/watch?v=ZjM9...ature=youtu.be

How to use it ?...