I wonder if Lucifer's baby, when he gave Castiel that power up, did something to him. It almost seemed like he was talking like a member of a cult after killing Dagon.
Maybe Lucifer is somehow able to communicate through the baby and is showing his version of a future just to ensure the baby doesn't get killed.
Besides, the Colt didn't work on Lucifer, why would anyone think it would work on hus baby? Even if it kills Kelly, the baby can resurrect her, which he has done already.
You know, I go back to the 5 things in creation that the Colt cannot kill line. Lucifer is clearly one, so that tells me Archangels. My theory on the others?
God and Amara, since they are the same kind of entity.
Death, creator of Reapers.
Eve, creator of monsters.
Leviathans, since they seem to be created by the same primordial soup as the Archangels.
Basically, anything that is an originator of others things, a creator, and since at least 2 are created from primordial soup (with Eve also appearing to be related to, or may even BE, a Leviathan), I have always thought as those are the ones immune to the Colt.
What do you all think?