There are very complicated laws involving the line between parody and copyright infringement--starting with the fact that the words "A PARODY" have to be much more prominent than you would think.
The idea is that you are free to make fun of something, but you are not free to capitalize on someone else's creative work. That's a pretty fine line.
If you don't consult a lawyer on this, as Phyllis suggested, you could easily be sued or shut down.
See below how clearly these books have to state that they are parodies, even if you or I would think the cover art makes that obvious: