It's hard to believe it could be a fake Castiel. Did you see how worried Zach looked (after he asked Castiel how he came back) before he peaced out after Castiel killed his hench-angels with what looks like the same type (or same) sword Uriel used on angels last year? What has the juice to bring back an angel that was turned into "a balloon of chunky soup" that exploded (Chuck's words)? Hint: God. That isn't something Lucifer is capable of (the bringing Castiel back part). I think it's possible, but slim, that Lucifer put the boys on the plane, but more likely that it was God that both brought back Castiel and put the boys on the plane, and was "no longer in the building" last season, probably because he was playing Skee-ball with Michael in New Jersey somewhere. I think the major problem God has with what Zach is doing is he didn't sanction it, and they sped up the timeline for the Apocalypse, so he finally is acting to prevent it. Dean being Michael's "angel condom" is more worrisome.. I don't want a superpowered Dean to kill or cast out/lock up Lucifer again.. as fun as it would be to see Michael. I'd rather Dean figure something out as a human and do it, or Michael take possession but leave Dean in the driver's seat.. I don't know...