Warning: The following contains SPOILERS for the first three episodes of Titans season 3.
What DC Comics villains could have ed forces with Jason Todd to help him become the Red Hood in Titans season 3? This question dominated the first three episodes of the HBO Max series' latest season, offering a worthy mystery for Dick Grayson and the rest of his superhero allies. As formidable as Jason Todd was as a former student of Batman, he would have needed help with at least one aspect of his transformation; cheating death with a literal resurrection or faking his death well enough to fool the world's greatest detective.
Jason Todd was apparently killed in the opening scene of Titans season 3 premiere, "Barbara Gordon," beaten to death by The Joker with a crowbar in imitation of Jason Todd's death in the comics. One episode later, in the climax of "Red Hood," Todd was revealed to be the mysterious new crime boss who was terrorizing Gotham City and blackmailing innocent people into committing crimes while wearing red hoods. This raised the question of just how Todd was alive two days after his violent death and who had been helping him with the aspects of his plan that seemed far beyond the capabilities of a hot-tempered teenager who wasn't known for planning ahead.
The only real clues the Titans had as to Jason's plan and the identity of his conspirator was a chemistry book in his bedroom at Wayne Manor, a notebook full of advanced chemistry formulae, and a secret lab in a largely abandoned building where Jason had been manufacturing some unknown chemical. This raised several possibilities, given that many of Batman's villains are geniuses and master chemists. However, there is still the question of whether or not Jason Todd actually died and was brought back from the dead a day later or if he found some means to fake his death.
Scarecrow
The most obvious villain to have allied himself with Jason Todd is Dr. Jonathan Crane, a.k.a. Scarecrow. Ignoring that the self-dubbed Master of Fear is a series regular in Titans season 3 (played by Mad Men's Vincent Kartheiser), he also fits the bill as a master chemist. While Titans' version of Scarecrow comes off as more of an erudite stoner than the bookish academic the character is usually portrayed as in the comics, he's certainly smart enough to have puzzled out Batman's secret identity and would almost certainly have begun exploring the connection between Batman and the police after being offered a job as a consulting criminal profiler while incarcerated at Arkham Asylum.
There are several other signs that point to the Scarecrow being involved in creating the Red Hood or at least aiding Todd in his plans. Chief among these is the scene right before Jason Todd went off to confront the Joker in Titans' season 3 premiere. Todd called Bruce Wayne, who was away on a business trip, and tried to convince him that he could handle Joker alone, saying that he was "not afraid of anything anymore" while eying a curious inhaler. He later used the inhaler as he was suiting up and seemed to become more aggressive afterward.
While Scarecrow is renowned for having created toxins that temporarily give a person specific fears or cause them to hallucinate their worst nightmares made real, some stories have also seen the Scarecrow create a formula that has the opposite effect, making a person fearless to the point of carelessness. It seems likely that Todd began using such a formula to overcome the fear-based flashbacks he experienced following his near death in Titans season 2. It's possible that Todd's new Red Hood persona is the result of Scarecrow's psychological manipulations, as well as his chemical formulas, and if there's any villain capable of corrupting Jason Todd and doing it purely for the sake of an experiment it is Dr. Jonathan Crane.
Blackfire
Another interesting possibility for Titans apart from Starfire before now, and a plan this complex seems even more uncharacteristic of her portrayal in the source material than it does for Jason Todd.
Ra's Al Ghul
One of Batman's most powerful enemies in of influence and longevity, Ra's Al Ghul commands a global network of assassins, considerable resources and the secret of the Lazarus Pit, which can heal any injury and extend a lifespan. Dove mentioned Ra's Al Ghul as a likely suspect in "Hank and Dove," as the Titans were pondering how Jason seemingly came back from the dead, but Dick Grayson dismissed his involvement as unlikely, somehow knowing that Ra's was currently in Kadeem. While the Lazarus Pit certainly could bring Jason Todd back from the dead, it seems unlikely Ra's Al Ghul or his agents would have been able to steal his body undetected, transport him to one of the Lazarus Pits and then bring him back to Gotham City within the timetable of the first two episodes of Titans. Additionally, there's no obvious motive for Ra's to bother himself with such a plan in the first place, as he has no need to seek revenge on the Titans and he'd likely see Jason Todd as a poor recruit for his cause in any case.
Talia Al Ghul
In the New 52 reality of DC Comics, Talia Al Ghul, daughter of Ra's, was responsible for stealing Jason Todd's body, resurrecting him in the Lazarus Pit, and seeing him trained by the All-Caste (a sect of warrior monks) and the assassins Bronze Tiger and Lady Shiva. Unlike her father, Talia felt Jason showed tremendous potential as a League of Assassins recruit, but Todd rejected the organization after learning that, despite Ra's Al Ghul's dogma about building a better world, most of his followers were less concerned with justice than acquiring wealth and power. However, it seems unlikely something similar has happened in the reality of Titans, given this story played out over several years in the comics and Jason Todd's transformation into the Red Hood took place over the course of three days.
The Joker
Perhaps the most horrifying possibility is that the Joker somehow engineered Jason Todd's breakdown as part of the ultimate revenge scheme. Certainly, the idea that Joker faked the death of Robin with the hopes that it would finally push Batman to break his one rule and kill the Joker and justify Joker's belief that one bad day can break even the most moral of men has merit. To his sick mind, the only thing funnier than corrupting Batman would be to corrupt Batman and have it turn out that it was all for nothing since Jason Todd wasn't really dead. Joker also had the chemistry background needed to manage whatever Jason was cooking in his secret lab and somehow brainwashing Jason into adopting his original criminal identity, the Red Hood, would be an extra added dash of drama worthy of the Clown Prince of Crime.
It's worth noting that the DCAU version of the Joker executed a similar scheme in Batman Beyond: Return of the Joker, brainwashing the Tim Drake Robin into becoming Joker Junior and implanting him with a microchip that allowed an electronic copy of his consciousness to take over Tim Drake's body as an adult. It's possible The Joker did something similar with Jason Todd during the three months between Titans season 2 and season 3, turning the Boy Wonder into his catspaw from beyond the grave.