Xox had been very careful not to use his celestial energy. Usually it wasn't an energy that one could recognise in the first place, unless there was another celestial. Maybe they could feel something was different but they wouldn't be able to pinpoint where that difference in energy was from, not while there was a large crowd around them.
At the same time, Xox's transformation skills were perfect. It wasn't some type of ability. The cells in his ball shaped body, literally transformed, so it was like that of the being he copied, even down to the smell. When he was a Mermerial no one would be able to tell a difference, even if they were to dissect him apart.
It was also true for his vampire form right now. He had even gone to the length of kidnapping a vampire, so he could copy the kidnapped individual's details. So the vampires wouldn't even bat an eyelid at what he smelled like.