The Antisocial Socialist

I think the producers hated mantis guy. Later on, JMS would write some "he took over as the criminal underlord since mantis guy was found dead in a spider hooker's room" or something like that to explain the absence.

Oh BTW, apparently JMS and the producers noticed that the extras were eating with people in the same costumes so they decided to make a Narn extra into a Centauri extra. It took him three days to switch lunch buddies. Three very uncomfortable days.