The epigram, "Hell is empty and all the devils are here," is from Act I, scene 2, of Shakespeare's "The Tempest." Ariel, the magic spirit who serves the sorcerer Prospero, is reporting to him what the king's son, Ferdinand, cried before abandoning ship and leaping into the ocean in terror from the storm - the tempest - that Prospero stirred up.
The episode's title references "Where The Wild Things Are", a 1963 children's book by Maurice Sendak. The protagonist travels to a fantasy realm.
Elizabeth Tulloch wore prosthetic makeup for the first time in this episode.
Oliver Keller, who portrays Blutbad, was credited for the first time; he has previously been a stunt double in several episodes and every season except for season 4.
Nick had a total of 12 bullets in the Mirror Dimension and fired all of them.