I think I'm going to freak out my friends in a forest while they are camping.
How are you going to freak them out?
I'll hide somewhere and then spring a surprise on them at night
It isn't very nice to scare your friends like that.  How would you like it if someone did that to you?
I think they'll find it very funny.
I don't think they'll find it funny, I think they'll be really scared. They might think that a wild animal is attacking them. I don't think you should prank your friends like this.