I think it would be interesting if Mercurial Knight Cookie had actually forgotten what he originally looked like due to the slime-like / liquid nature of his body — something he gained after the Silver Blessing. Little by little, everyday since taking the oath, his visage changed in subtle ways. Especially every time he was injured; though he could always reform, his "true" form continued to become more distorted and muddled. It warped entirely into something else overtime. The way he looks presently ( read: exhibits and manifests himself ) is completely different from what he looked like originally, and many years from now his visage will have changed just as much again.
Also! When he's more seriously injured, it takes extra time for him to reform, and the process can look monstrous. Like the blob of a melting body whose features and appendages stick out in odd places... It takes time for everything to align properly again.
