Question: What is the origin of the magic cupboard?
Question: Has it ever been known where the magical key came from and what other magic it might possess?
Answer: In the books, yes. The key was a copy made for a theft, but because it was made by a psychic who practiced her craft by pouring molten lead and "reading" the shape it took upon cooling, the key was imbued with magical power. Specifically, it could be used in any "lever lock" style lock and it possessed the power to facilitate time travel derived from the psychic's ability to see the future. The cupboard itself also had the power to bring plastic things to life because the psychic's nephew, with his own latent psychic abilities, built it to contain his hatred of all things plastic (he was an out-of-business toy manufacturer who made lead soldiers around the time plastic toys became popular). He cast his hatred into the cupboard and locked it with his aunt's magic key. So now, that cupboard when used in conjunction with that key, will imbue a plastic avatar with the consciousness of a human being from some other point in time. When the key is used to lock a person inside any other sufficiently-sized container, that person's consciousness will be sent into a suitable avatar, also at another point in time.
Answer: The cupboard isn't magical. It was found by Omri's brothers in the alley behind their house and given to him for his birthday. The magic comes from the key, which Omri's mom gave to him after seeing the cupboard. It originally belonged to either her grandmother or aunt, I forget which. In the books, Omri is able to use the key in other objects (like a trunk) proving the key has the magic, not the old cupboard.
Kaitlin Schwartzel