Horror movie prequels are a dime a dozen. Some, however, are actually worth watching more than once.
Maybe you can't get enough of The Texas Chainsaw Massacre: The Beginning because you got an inside look into the workings of the Sawyer family's past.
Or you rewatch Final Destination 5 over and over again because the fact that it's a prequel is the surprise twist ending.
Perhaps Amityville II: The Possession is what spawned your love for a good prequel because you get to see the murderous events that took place at the Amityville house before the DeFeos moved in.
