At the comic convention, there is a man in a blue wizard costume seen over Danno's shoulder walking towards him, from about 15 feet behind, just as Danno turns his head. As the camera angle changes, the man in the blue wizard costume has already passed Danno and is passing McGarrett. There is no way he could have traveled that far in less than half a second.
While at the convention, the person dressed in the Star Trek DS9 uniform says he is Commander Sisko, but his baldness and goatee is the look Sisko had when he was a Captain.
While at the convention, the person dressed in the Star Trek DS9 uniform says he is Commander Sisko. The insignia on his uniform is that of a Captain, not a Commander.