Travel between different universes can be a tricky thing. Sometimes, time passes more quickly in your home universe, so that when you return from a trip to another one, everyone you know is dead. Other times, you can spend weeks, months, or even …| TV Tropes
You have to Be Careful What You Wish For, because oh boy are you gonna get it. More often than not, a wish-granting entity (genie, vengeance demon, holodeck, leprechaun, and so on) has some sort of contractual clause stating that they have to …| TV Tropes