He was told to lay low after all, so unless the plan already changed I can’t see him disobeying orders of his own volition, and it’s pretty clear Emerald did make eye contact with Ruby.
Actually it isn’t all surprising if he disobeyed, in RWBY vol 2 ep 1, Mercury and Emerald were told to keep a low profile in vale and they had went to take care one of Roman’s job. If he decided to do things himself then he is in trouble.
The second, and I may be grasping at straws here, is that Mercury is just another of Emerald’s illusions.
Emerald’s illusions may be people and can make sound, but they dissipate as soon they come into contact with something, like Blake’s or Neo’s stand-in’s
which could suggest that she can copy other people’s weapons from special photographs, with the bulk of the box acting as a “3D Printer” of sorts, and that the thing she had “built up” by the end of Volume 2 was a stockpile of weapon photographs.
if that is true then it could be she is master in a variety of weapon combat styles, but once she used one she can’t use it again, needs a new image or “refresh it” by taking another image.
