There are plenty of good reasons to visit Mezcal. The tequila list (200+). The crowd (Colfax-neighborhood-cool). The food (dollar soft tacos for happy hour!). But now I have an even better reason to drop in on Saturday nights: Mariachi Vasquez. I popped in around 11 p.m.  Saturday night, and the place was packed. My friend and I found a single empty bar stool and claimed it as our spot at the bar, and soon we understood what everyone had been waiting for. Six members of Mariachi Vasquez picked up their assorted instruments (guitar, trumpet, trombone and violin) and proceeded to serenade the crowd with their particular blend of Latin/acoustic/hardcore music. I'm told that they normally stroll around from place to place inside the restaurant, but during my visit they pretty much claimed a corner and remained there; it could be that the space was simply a bit too full to allow a large group to wander around much. For now the group performs at Mezcal as special guests, but the folks at Mezcal like them so much -- and the party vibe the band adds to the atmosphere -- that soon they hope to bring them around on a weekly basis every Saturday.