Its a very easy and short minigame: You have to talk to Mr. Ghost who is at the varanas west teleporter, then he transforms you into a ghost. You have to walk around and scare other people (npc) with an extra buff. You need to start scaring children first, if your buff has stacked higher you can start scaring adults and if your buff stacks up even more you are able to scare old people.
Personnaly my experience is, that it's also easier to scare girls (women) than boys (men)
The goal is to let your buff stack as high as possible. Sometimes it happens, that you won't scare them which let your buff decrease.
Greets