The trailer for Titans' season 1 finale depicting a battle between Dick Grayson and a Batman gone mad is clearly a dream sequence. This fact was pretty much confirmed by an episode synopsis later released by DC Universe, but the unreal nature of the trailer is made obvious through careful consideration.
"Koriand'r", the penultimate episode of Titans' first season ended on a cliffhanger with Dick Grayson, Donna Troy and Kory Anders (Starfire) rushing to return to the farmhouse owned by Raven's mother. Earlier in the episode, Starfire recovered enough of her memories to recall why she had been sent to Earth in search of Raven - to stop her mother from using Raven as a means of drawing her demonic father Trigon into the material plane. Unfortunately, this revelation came too late, as a frantic Raven was convinced to call out to her father for help in healing a wounded Beast Boy - wounds that had naturally been inflicted by Raven's mother in secret. The episode ended with a mystic barrier keeping Donna Troy and Starfire from following after the former Robin as he entered into the farmhouse.
Given this ending, fans were confused when the trailer for Titans' season finale depicted Dick Grayson being approached by a wheelchair-bound Jason Todd and being informed that Batman had gone over the edge following Commissioner Gordon's death. The trailer also depicted a SWAT team storming Wayne Manor and a suggestion that Batman had killed (or was ready to kill) the Joker. This would have presented an amazing number of changes to the Batman mythology, which would be surprising given how little Titans has touched upon Gotham City apart from introducing Jason Todd as a character in its sixth episode.
Granting that Titans has seen some wild and sudden shifts in its storyline from episode to episode, this would seem to present too many major changes too quickly. It is one thing for Titans to suddenly air an origin story for Hawk and Dove one episode after ending with a cliffhanger of Starfire strangling Raven. It would be quite another thing for the series to suddenly turn Batman into a mad-dog killer, without any prior indication that Bruce Wayne would be appearing on Titans, much less that the status quo of the character would be shifted so drastically. Such a change would be unlikely to occur in the finale of a Batman series, much less as part of a show focused on the Titans!
Of course, that's not what's going on. The Titans season finale synopsis makes clear that this is supposed to be all part of the grand season-long plot, with Robin in a dream:
"In the season finale, Trigon’s powers send Dick into a dreamscape that begins with him living a happy domestic life, but soon takes him into a dark journey back to Gotham."
Indeed, a scenario such as the one we see in the Titans' finale trailer only makes sense within the context of Trigon attempting to play with Dick Grayson's head and forcing him into some kind of nightmare. Why he should choose to focus on the former Robin and allow him into the farmhouse remains to be seen, but it seems likely Trigon will attempt to force Raven to choose between her biological parents and the foster father figure who took her under his wing. Hopefully, the truth of things will be revealed when "Dick Grayson" airs this weekend on DC Universe.