The Horrible Changing Stone

The Changing Stone: A small smooth stone that can fit in your hand. It seems normal, but glows when the holder utters a wish. However, those whose wishes are brought to life by the stone often realize that the stone has twisted them so that they are not as enjoyable as they thought they would be.

The stone is indestructible, and there is no limit to what it can do. You do not have to say "I wish" to activate it, simply thinking "I want" can cause changes, however thinking about what you want will make the stone's magic work more subtly while outright wishing for something will cause a drastic shift.
The stone's magic is not apparent to anyone but the one who caused it, unless the user wishes for someone else to be aware of the magic too.