Warning: The following contains SPOILERS for Titans season 2, episode 13, "Nightwing."
The season 2 finale of Titans sets up season 3 by introducing a newly united family of Titans and bringing Blackfire to Earth. The newly christened Nightwing is now firmly established as the team leader, while the episode also reveals the villain who will likely be next season's big bad.
Titans' season 2 finale brought about a more definitive end compared to the season 1 finale, which ended on a cliffhanger with its chief villain undefeated. The long-awaited battle against Raven's father, Trigon, would not come until Titans' season 2 premiere and was widely regarded as an anti-climactic mess. By contrast, the season 2 finale resolved most of the season's major storylines and saw Deathstroke defeated and the newly born Conner (aka Superboy) freed from the clutches of Cadmus.
The episode ended with the Titans on firmer ground and the team largely restored to its former glory. While Hank Hall and Dawn Granger seem to have finally ended their on-again, off-again romance, the two did agree they could continue to fight crime together as Hawk and Dove and remained with the Titans. Kory Anders (aka Starfire) remained with the team as well, despite her energy generation powers having mysteriously stopped functioning. The team was also joined by the newly freed Superboy, his super-dog Krypto, Gar Logan (aka Beast Boy) and Rose Wilson (aka Ravager) who is now sharing her body with the mind of her body-possessing half-brother Jericho.
It is good that the team have reestablished their strength, because the Titans season 2 finale also set up a new challenge for them in season 3. The final scene of "Nightwing" revealed the arrival of Blackfire, the sinister sister of Stafire, who takes possession of the body of a young mother in a grocery store parking lot. The scene ends with the mother's body reshaping into that of Blackfire and Blackfire walking away from the minivan containing the woman's two daughters, her eyes glowing an ominous dark violet.
Blackfire appeared earlier in the season in Titans season 2, episode 9, "Atonement," after having taken possession of Kory's former bodyguard, Faddei. Kory realized something was up, however, and gave Faddei a merciful death. It was then that Blackfire revealed herself through a holographic projection and confirmed to Kory that she had killed their parents, claiming the throne of their planet for herself. While Kory swore vengeance and declared that she would be coming for Blackfire, it seems that her sister has elected not to wait for Kory to return to Tamaran and will be bringing the fight to her in Titans season 3.