A short Let's Play preview from the McMillens
Here's Edmund and Danielle McMillen previewing cooperative play in The Binding of Isaac: Rebirth including one of the game's twenty challenges, Head Trauma, in which you have tons of tears spraying all over the place but they're low-powered.
For this playthrough, Edmund was the co-op partner and as luck would have it, he ended up being the Troll Baby, who drops bombs uncontrollably every so often. Stick around for a short encounter with the boss Dingle, a happy-go-lucky poop with mini-poops.
No release date yet, darn it.