What Dark Tower references can you see (from Stephen King's series)?
WARNING: POTENTIAL SPOILERS BELOW
1. The door in the middle of nowhere in Season 4 is just like those that Roland finds on the beach in book 2. He goes through the three doors to be inside the heads of three different characters.
2. The horshoe crab could be one of the crabs from book 2...
3. Reverend Flagg and Randall Flagg...one and the same? And is William the Randall/Reverend Flagg in this world?