The weirdest scene in the Titans season 2 premiere saw one Robin shoot another using the gun that killed Batman's parents. Picking up from the season 1 cliffhanger that was never supposed to happen, Titans season 2 opened with most of the team placed into dream-like states by the villainous demon, Trigon. Using the Titans' own fears and faults against them, Trigon manipulated the heroes into accepting their darkness, and thus enslaving them to his will, all in the name of conquering the universe.
As part of these strange sequences, the Titans season 1 finale saw Dick Grayson in a reality where he fought and killed Batman after deciding that the Caped Crusader had finally gone too far. To corrupt Jason Todd, Trigon decides to warp the second Robin into the same alternate reality as Grayson, popping him in right at the moment his predecessor is standing triumphantly over Batman's corpse. Naturally, the two Robins begin to do battle, and this is the fight seen in the Titans season 2 trailer that caused much speculation prior to the episode's release.
As one might expect, Dick has the beating of the younger and less experienced Jason and is in complete control of the fight. However, it's pointed out that the Batcave contains a particularly unique memento. Sitting on a desk near the Bat-computer is a revolver on a stand, which turns out to be the very gun Joe Chill used to gun down Bruce Wayne's parents. The millionaire evidently now keeps this as a reminder of his ongoing mission. In the Robin vs. Robin scuffle, the gun is knocked from its perch and Jason is first to react. Unable to beat Dick with his hands, Robin mk. II shoots his opponent straight in the head.
While all of the Trigon visions in Titans' season 2 premiere are strange, this is by far the weirdest. More than Dawn and Hank getting high or Wonder Girl remembering her origin story, the battle of the Robins is a mish-mash of rivalry, respect, jealousy and anger, and is settled with the weapon responsible for both characters becoming superheroes in the first place.
In the Batman comic books and other live-action interpretations, Joe Chill's gun isn't usually a staple of the Batcave's decor, but there is precedent for its presence in Titans. In Detective Comics #1000, an incognito Bruce Wayne seeks out and purchases the infamous firearm, but ultimately decides to melt it down, rather than keep it on display. In the 2017 Justice League movie, however, a gun can be seen in a display case during one scene set in the Batcave, and one would naturally assume this would have belonged to Joe Chill.
It remains to be seen whether Titans' version of Batman genuinely does have Joe Chill's gun on display in his home, and this is why it was part of Dick's vision, or whether the item was merely part of Trigon's manipulation - providing Jason Todd with a tempting way of defeating Dick Grayson.
Titans season 2 continues with "Rose" September 13th on DC Universe.