The Pack are sushi zombies.It's mentioned in "When Will Ben Be Zen?" that the members of the Sushi Pack were created by a lightning storm. Formerly raw fish jolted to life by lightning...
The Prevaricator that the Sushi Pack took down in "Where No Truth Lies" was not the real Prevaricator.As The Sushi Pack learns, The Prevaricator is a master liar. Big lies, white lies, sweet little lies, stone cold lies, etc., he's mastered them all. But when they actually encounter The Prevaricator, all he does is contradict their statements and say the exact opposite of what he means. This is because the man they encountered was actually a decoy. According to the episode, The Prevaricator has been after Mayor Martin's collection for years, yet hasn't been able to get it, despite being a master thief. So the real Prevaricator hired a random thug in order to get it, and gave him instructions on how to be "The Prevaricator," which the thug didn't quite get.