My favorite character to voice comes back in episode 32, Play Within a Play. And why not? It's all about acting, after all. Interested in the effects chain on Brando's dialog? What do you mean you're not? Screw you, I'm explaining it anyway!
There's a flanger, which is an effect I think adopted early on, or perhaps invented, by the Beatles. If I remember the story correctly, John was too lazy to double-track his vocals, so instead they copied the track over and then applied finger pressure to the tape as it went through the heads, slightly slowing it and letting it speed up. These days, it's automated, and you don't have to finger any tape. It creates a distinctive swishy sound that's also great on drums in psychedelic freakouts.
There's also a delay, and the little plugin I use for it dampens the high end on subsequent echoes, which is nice because a straight up digital-style delay would be, I think, distracting.
My only challenge now is not overusing our friend Marlon. But sometimes I just can't help myself.