Titans Theory: Jericho Has Possessed Deathstroke's Body
Could Slade Wilson's vendetta against Dick Grayson and his teammates on Titans truly be the work of Jericho possessing the body of Deathstroke? While such an idea may seem outlandish, there is precedent for it in the original Teen Titans comics. Such a daring plot twist would also explain certain incongruities in Deathstroke's behavior over the season so far.
The plot of Titans season 2 has centered around Deathstroke coming out of retirement after learning that the Titans had reformed. While the full history between Deathstroke and the Titans has yet to be explained, the flashback episode "Aqualad" revealed that Deathstroke was responsible for the death of Aqualad. It is unclear, however, if Deathstroke was hired to kill all of the Titans or if he was targeting Donna Troy or Aqualad - both of whom could be valid targets for an assassination, given their relationship to the royal families of two powerful nations. In any case, the episode ended with Dick Grayson determining that Aqualad's killer was Slade Wilson and approaching Slade's son, Jericho, in a record shop. It was later confirmed in season 2, episode 5, "Deathstroke," that Dick befriended Jericho with the intention of using him as a means of getting to his father.
This is revealed as the elder Titans discuss how to handle Deathstroke's ultimatum that they turn over his daughter, Rose Wilson, whom Dick Grayson placed under his protection in exchange for the release of the kidnapped Jason Todd. While Jericho's fate is not revealed, Dove says that the team has gone down this path before and that they are not "using Deathstroke's kid to get to him again." Another clue as to what happened to Jericho was revealed as Slade speaks to Jason, telling him that he is "being played by that charlatan, Dick Grayson, who gives costumes to foolish kids, making them believe that they're heroes. Leading you, like lambs to slaughter."
This all suggests that, as in the original Teen Titans comics, Jericho joined the Titans and died while fighting his father. Ironically, Deathstroke killed his own son as an act of mercy after Jericho became possessed by hostile spirits. While Jericho's body died, his soul was freed from their corrupting influence and wound up taking residence in his father's body, though his personality lay dormant for many years.
Jericho "woke up" after Slade learned of the death of Donna Troy and the formation of a new Teen Titans. Taking over his father's body, Jericho had planned to reach out to his old friends and convince them that teenagers should be teenagers and should not try to be superheroes as they had. Unfortunately, Jericho had grown mentally unstable after his trials, and wound up attacking his friends while playing at being Deathstroke seeking revenge.
These circumstances seem nearly identical to the story of Titans season 2 and how Deathstroke came to resume his war on the team, suggesting that Slade Wilson is being possessed by an embittered Jericho, who hates the Titans for betraying his friendship and causing his death. This would explain why Slade seems so focused on Dick Grayson over the rest of the Titans and why he seemed so distant in his interactions with Wintergreen, who is supposed to be his closest friend and brother in arms. It's also probably not a coincidence that the Teen Titans storyline that saw Jericho return from the dead while possessing Deathstroke's body was written by Geoff Johns - one of the writers and executive producers of Titans.