User blog comment:FairyRaven/Fairy Tail Chapter 357: The Nine Demon Gates, Review and Commentary/@comment-112.198.64.42-20131027154249/@comment-4829046-20131027163734

Only Silver was stated to be in his human form among the Nine Gates. I think all of the more sentient Demons in the series can change into a full human form or a flute in Lullaby's case.

But I do love transformations, even though Doriate's one was lacklustre.