The Space Egg from JLA/Avengers.
We all know that it has surfaced in DC and brought back characters that died in both JLA/Avengers and continuum in DC, The Crime Syndicate. Some people are saying that Marvel isn't counting it, but I believe they are...
I personally believe this Egg is affecting both universes on a major scale..
First off, seeing as it brought those guys back.
I also suspect it has been bringing back other characters from time's past.
Batman himself said the new Supergirl isn't right, she shouldn't be here, and she shouldn't exist.
Next, there's the fact that the DC/M-Universal polar opposites in Batman and Captain America, who both lost a side-kick... regained them - AT THE SAME TIME. Coincidence? I doubt it, but probably. In the MU, Thanos was supposed to make it impossible for this to happen when he was all powerful. No dead characters are supposed to return.
I have a lot of other theories, but some of them are less tangible... I'm not sure..
Any ideas, or other theories for either/or/both Universes?