Raven's mother, Arella, appears in this episode. Angela Roth, involved in a mystic cult, was chosen to become the bride of the demonic Trigon. Abandoned by the demon after mating with him, she was taken in by the pacifistic disciples of Temple Azarath, a group who had centuries earlier forsaken life on Earth to pursue their own nonviolent lifestyle. Angela was given the name "Arella", which means "messenger angel." In their interdimensional world, Raven, Arella's daughter by Trigon, was born. Raven grew up on Azarath and learned to control her emotions, lest Trigon's evil would burst free. In the comics, Raven and Arella's story was told in "The New Teen Titans" (vol. 1) #1-6.
In the comics, Raven would sometimes let her evil side show - which sometimes would cause her own teammates to fear her. Eventually, Raven became increasingly corrupted by Trigon and became the vessel that brought him to earth. Once on earth, Trigon lay waste to the planet until he was eventually destroyed by the combined forces of the Teen Titans. It all happened in "The New Teen Titans" (vol. 2) #1-5.
At about 6:45 into the episode Raven is hovering in front of a townhouse owned by Dr. Stephan Strange. Look at the skylight.
Raven mentions, "I'm not just a person. I'm a portal." In the comics, when Raven was reborn in a new body by Brother Blood, one of her new abilities was to act as a 'doorway.'
Other references from the comics in this episode include: Trigon lay waste to Azarath from "The New Teen Titans" (vol. 2) #1-5, The 4-eyes is the mark of Trigon, and The sculptures in the library look like the Azarathians from the comic book series.