User blog comment:Rafe Adler/"Stuck in the Middle (With You)" Discussion/@comment-1031724-20170217183659/@comment-1031724-20170218010343

I figured Azazel would have been immune to the knife if Alastair was, since he was the initial ruler of the demons (but then, Lilith was in hell) and is immune to holy water. Now it's confirmed the knife doesn't affect Princes of Hell. Princes of Hell, Knights of Hell, and the white-eyed demons seem to be the most powerful that are harder to kill, though we know the Colt and the Lance of Michael can kill Princes of Hell and Sam's demon-killing power can kill white-eyed demons. Both of the ones we've seen, as a matter of fact - Lilith and Alastair. Do they have an official title? We know Lilith is Lucifer's first, but why is Alastair like her? He's obviously lower-ranked than her because Lilith knew Ruby was on her side and Alastair didn't.

Do angel blades work on them too? I'd like to think so, angels have always been more powerful than demons, even though there has been at least one instance of a demon killing an angel.