Notice that Artie Lange lost a signifigant amount of weight between the pilot and the main set. It stated in his autobiography that he used drugs to lose weight.
Bryan Callen was added to the cast at the last minute, replacing Craig Anton as the eighth cast member. This explains why Craig Anton appears in the opening sketch and Bryan doesn't. Anton remained on the show as a featured player for three years.
Sketch: "Deep Stain Nine"
This sketch spoofs the 1990s TV series Star Trek: Deep Space Nine.