Not every show can have the luck of Friends or Seinfeld and keep its main cast in place for an entire run. Career decisions, creative changes, and just plain boredom can cause a show to shuffle its deck and present a slightly tweaked -- or downright unrecognizable -- mix of old and new characters. We tapped into our TV brains to come up with some of the best and worst late-season additions for a few of our favorite shows.
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