Like you tell everyone they will have practical jokes played on them.
Then you message a few guests individually and ask them to participate on practical jokes on other guests. This wins you their trust and creates an atmosphere where everyone thinks they're safe as their in on a joke on somebody else.
Eventually near the end of the night you pretend to stab yourself then everyone gets really worried then you stand up and go SURPRISE!
This leads me onto my next invention: like a retractable knife that retracts when you stab something with it like a telescope. Also in the handle there would be some fake blood so when the blade popped back out again it would look realistic.
Thanks. Gonna go buy some Big Match Cans and watch korea get humped.