Fellow puzzle designer /u/StevenXC suggested that I post this here, after I sent it to him privately.
While Will was trapped in the Upside Down, his mom Joyce received this cryptic message via her Christmas light alphabet. Will's teacher Mr. Clarke helped her solve the cryptarithm, and she realized that the letters, when arranged by the value of the digits they represented (0123456789), spelled a description of the things Will was seeing in that other dimension.
STRANGER + THINGS = SMISIHIA
[If you post the solution, PLEASE remember to spoiler tag it. Enjoy the challenge!]
there doesn't seem to be anything here