CMDU: Batman.

While the two universes collided Batman was in the Bat-Cave fixing some gadgets. He heard a little earthquake and went out to control. He was surprised when he saw villains he never saw, Cottonmouth, Rattler, Puff Adder and Death Adder, spreading panic in Gotham. With the help of Nightwing, Red Robin and Robin he beated them and went to the Justice Hall looking for answers. The first thing he noticed was a couple of new buildings (the Stark Tower and the Baxter Building) next to the Justice Hall. When Superman came back from his mission in the space he said what happened with Krona and Batman understood their universe was merged with another one. Bruce started keeping in touch with other heroes (like Iron Man, Spider-Man, Captain America etc.) helping them fighting crime and looking for informations about the collision. Now Batman and Superman founded the new JLA but when Wonder Woman decided to add Protector in the team Batman gathered his Outsiders asking help to Geo-Force and Metamorpho if Protector would loose control.

After some days Spider-Man was called by Batman who wanted informations about a strange vigilante with a strange black suit. Batman showed Spider-Man the pictures he found and Spider-Man recognized the vigilante as Agent Venom aka his long life friend Eugene "Flash" Thompson. Spider-Man explained Batman who he was and spoke also about the symbiote. Batman asked Spider-Man to tell him informations about how to destroy the symbiote but Spider-man disagreed as Flash could died because he spent to much time with the symbiote and being divided from it would kill him. Batman understood Spider-Man was personally involved in the situation and thought he was lying so he insisted but Spider-Man refused to tell him. It ended with Spider-Man quitting the Outsiders and Batman having two new problems: the new vigilante and the only one who knows how to beat him.

As Batman saw a fight between the Outsiders and the Slingers as last resort he prefered another way to end this senseless battle. He asked Superboy to gather the Ravers and help him and the Outsiders to surrond the Slingers (as it would be 14 against 7 people) and force them to give up. Batman was surprised by Conner's determination of fighting his friends to do what's right and congratulated him. But his plan didn't go the way he thought it would.

15/05 Update: I added the story where Spider-Man leaves the Outsiders.
09/07 Update: I added the story when Batman asks Superboy to gather the Ravers.

-Batman.