It appears as though Marcel, after Sebastien's death, dedicated his life to 1) giving himself (and later, his partners the Pathologist and the Geneticist) the powers of electromagnokinesis, longevity, and memory manipulation, and 2) resurrecting Sebastien/The Beast of Gevaudan.
Lydia uses her scream as a weapon for the first time since she was rescued from Eichen House in Lie Ability. The last time she purposely used her scream as a weapon was in The Sword and the Spirit during her attempt at escaping Eichen.
Corinne expands on the story of Malia taking her powers during childbirth and implies both that Talia Hale acted as her doula and that Werecoyotes do pass on part of their powers to their offspring in general. The fact that Malia supposedly took part of Corinne's powers in childbirth was first revealed in The Sword and the Spirit.
It is revealed that Theo did indeed gain Josh and Tracy's powers after killing them when he uses Josh's electrokinesis against Deucalion and Tracy's Kanima venom against Scott and Liam.
Scott receives the voicemails Kira left for him in The Beast of Beacon Hills in this episode, which eventually gives him the strength and determination he needs to rally the pack and finally defeat the Beast and Theo.
Deucalion reveals that not only has he been working with Scott and the McCall Pack since before Theo and the Chimera Pack tracked him down, but that he lied about his healed eyes being reverted back to their previously injured state, and he's actually had his eyesight this whole time as well.
This is especially ironic because in The Beast of Beacon Hills, Scott told Theo that he shouldn't trust Deucalion, which Theo took to mean that Scott believed Deucalion to be evil, when in reality, he was hinting that Deucalion would ultimately betray him.
Additionally, Deucalion reveals that Belasko's talons would have worked to take the Beast's power, and that what he told Hayden about them killing Theo was also a lie. This was confirmed when Malia uses them to take the rest of the Corinne's powers.
It is confirmed that shapeshifters with accelerated healing abilities can survive and heal from spinal injuries when Deucalion snaps Theo's neck. This was previous implied in Damnatio Memoriae, when Liam fell into the ravine and landed on a boulder so hard that he broke his back.
Chris Argent reveals to Gerard that he and Scott have also been working together this entire time, and that he knew that when he saved Gerard, that he'd only be concerned about immortalizing the Argent name rather than saving innocents from the Beast. Gerard was cured from his illness with yellow wolfsbane and brought back into the fold in Damnatio Memoriae.
Malia references the death of her adoptive mother and sister, which was first revealed in Season 3B's Anchors.
Allison Argent makes an appearance in this episode when Sebastien accidentally performs the memory-sharing ritual on Scott when he put him in a choke-hold, and Scott's mind, believing he was going to die, flooded with memories of he and Allison, including:
Allison relearning how to shoot with her bow and arrows after the effects of the surrogate sacrifice ritual in Season 3B's Anchors.
Scott and Allison cuddling in Allison's car while they guard Jackson (who was locked in a stolen prison van in the nature preserve to prevent him from attacking people in Kanima form) in Season 2's Frenemy.
Scott wiping a tear from Allison's face at the animal clinic after she hit a dog with her car in Season 1's Wolf Moon.
Scott cradling Allison's dying body after she was stabbed by an Oni in Insatiable.
When Stiles and Lydia discuss what happened with Sebastien seeing into Scott's mind, they realize that Allison and Marie-Jeanne must have looked exactly alike for Sebastien to have mistaken them. Marie-Jeanne first appeared in Maid of Gévaudan and was played by Crystal Reed for this exact reason.
Scott finally gives Hayden the bite in this episode when Deaton worries that her inferior Chimera healing abilities may not allow her to survive her serious wounds from Sebastien. Scott was first asked to give Hayden the bite by Liam in Lies of Omission and Status Asthmaticus.
Kira returns to Shiprock, New Mexico to train with the Skinwalkers and finally learn control over her inner Fox spirit as part of her deal with them to reassemble her katana and save her friends. She first went to the Skinwalkers in Damnatio Memoriae.
Scott returns to the library to see the initials the packmates wrote during Senior Scribe on the bookshelf, which occurred in Creatures of the Night.
The episode ends with a scene at the shed where the Dread Doctors had hooked Mason up to the tank of green fluid. Since the Dread Doctors' death, Der Soldat (the Nazi soldier and Alpha Werewolf who fought in World War II) had no supervision and was able to escape from his tank, suggesting he will be part of Season 6. His story was first explained by Theo in The Beast of Beacon Hills when he informed Scott and Liam that the Dread Doctors had been using him to extend their lifespans.
The episode title, "Apotheosis," means, "the highest point in the development of something; a culmination or climax," according to Merriam-Webster's dictionary. An example is, "His appearance as Hamlet was the apotheosis of his career." The word "apotheosis" also means, "the elevation of someone to divine status; deification."
It is revealed that despite Tracy being a part-Werewolf, part-KanimaChimera, she does not possess the power of pain absorption like most Werewolves and Werewolf-Chimeras have.
Theo is dragged underground by his deceased sister, though it was not explained how she was able to do this. Theo's fate is also unknown, as it was not shown if he survived what his sister did to him or not.
This episode marks the last appearance of Arden Cho as Kira Yukimura, as she announced after this episode aired that she is leaving the show.