The mask requirement also has some stipulations. Under California guidelines, not all face coverings will be permitted at Comic-Con. The event has a page on its website specific to these concerns. The only masks that are allowed are those that “fit properly and snugly,” are secure under your chin, and cover your nose and mouth completely.
They also must be visible at all times regardless of your cosplay. Basically, we might be seeing a lot of Kakashis this year. Mezo Shoji, anyone?