Dark Cyborg taunts his counterpart by saying he does not have a mother. In the comics, Cyborg's mother was killed by the plasma creature that also necessitated Cyborg receiving his bionic parts.
In the comics, Slade was initially the Titans adversary known as Deathtroke, the Terminator. But after his contract with the H.I.V.E. to kill the Titans was dissolved, Slade gave up his vendetta. With his son Jericho as a member, Deathstroke even became the Titans ally, especially when the team was abducted by the Wildebeest Society. This happened in "The New Titans" #72-84. Deathstroke remained a sometimes-ally for quite a few years after that. This is similar to how Slade teams up with Robin, the Titans he respects the most, in this episode.
"The End" parts 1-3 were inspired by the comic book tale, "The Terror of Trigon" which originally ran in "The New Teen Titans (vol. 2) #1-5. In this story, Raven had to fight Trigon's dark influence over her and this dark side grew as she exposed emotions. Eventually, Trigon came beckoning to Raven and she could no longer resist. Trigon's presence was unleashed! Many elements are borrowed from that original story in this episode. The earth after Trigon's emergence is similar to the comic book story. Flesh becomes stone. The skies burn red. And during Robin and Slade's journey, they pass walls of twisted flesh.