The scene where Alex (Chyler Leigh) pokes Lena (Katie McGrath) with a stick was scripted, however, Katie didn't know when it was coming.
One of the names Julia writes in the cave is Peter David. David was a writer on the supergirl comics for many years.
In DC comics the Kryptonian Demon is a deity as Krypton had its own Hell and demonic entities that were destroyed along with the planet.