Complex sentence: Also in 2013, they began offering the "Box of Dread", a random package full of merchandise delivered monthly to subscribers, one of whom is randomly chosen to receive a "special edition" valued at $250.
Split into simpler sentences: Also in 2013, they began offering the "Box of Dread", a random package full of merchandise delivered monthly to subscribers. Each month, one random subscriber is chosen to receive a "special edition" valued at $250.