At Comic-Con, Advice to Actors SAN DIEGO - "Don't come up to me in bathrooms." That was the first piece of advice for aspiring actors from Roger Mussenden, the casting director whose credits include "X-Men: First Class." At the Comic-Con International fan convention, Mr. Mussenden spoke to an attentive audience about a subject that does not usually get much attention from the costumed crowd here: the gritty realities of movie and television casting. Mr. Mussenden was joined by Randi Hiller, the vice president for casting at Walt Disney Studios; Sharon Bialy, whose credits include "Walking Dead"; and David Rapaport, of "Arrow" and other shows. The talk was moderated by Lora Kennedy, the executive vice president for casting at Warner Brothers. The audience mostly identified themselves as working actors, and only one of whom appeared to be wearing felt boots and a mask; these were serious types, looking for a path to the screen. Mr. Mussenden and company did their best to show the way, while describing its many pitfalls. If you want to be a superhero, "don't play the powers," Mr. Mussenden said, who added that he sees enough mutants and is looking for character, not electromagnetic fingertips or whatever. He illustrated his point by waving arms and hands in an impressive display of mock superness. Ms. Bialy reminded actors not to get carried away with themselves. "It's not about you," she said of that moment on the screen. It's your time to honor the text and move the story along. The panel also agreed that executives, producers and directors have a bad habit of overlooking the best advice from their casting advisers. Chris Hemsworth, they noted, was the first guy seen for "Thor," and an obvious choice. But it took a long time and a wide search before those in charge recognized that. Mr. Rapaport estimated the number of people who have a voice in the typical co-star casting decision at about 45. "Oh, my God!" gasped someone in the audience. One questioner asked what advice the casting folks might have for directors. "Take an acting class," Ms. Hiller said.