It never fails to amaze me when I read through these reviews and people point out things that are unrealistic. What do you think you're watching? The Mongolians are there for the same reason the kids travel to China via school bus - because it's absurd. If you don't find absurdity funny, fine, but you're watching the wrong show.
The only reason my rating is a 9 and not a 10 is I think the Great Wall plot ran a little too long. The rest of the episode was pure genius. Randy is my favorite character.