Pranks to do on my sister and her friend?

I would go into their room and say "have you seen my friend? Shes gone missing and I checked everywhere in the house" but your friend is really sitting in a dark corner with a mask on. And when your sister goes looking, she will go into the room sooner or later and then your friend can jump out and scare them both.

draw on their faces when they are asleep and be mean to them in the morning