In the SECOND EPISODE EVER of Night Court, a crazy ol' drunk claiming to be Santa Claus gets taken downtown, but it's gradually revealed that he knows everything about everyone's childhoods, down to the last intimate detail. Then he offers Harry Anderson the opportunity to succeed him as Santa. Again, this is the second episode, and they have already established that this courtroom exists in a world where Kris Kringle wants the judge to take over as the actual, real Santa Claus. And the next 191 episodes take place with all the characters in the show knowing that.
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In Home Improvement (in the very first season!), Mark starts questioning Santa's existence after Brad and Randy tell him that Santa died before he was born. "Wilson" then shows up dressed as Santa and gives everyone early presents, thus restoring Mark's faith. As Saint Nick leaves, Tim remarks that it's really nice of his neighbor to do something, only for Jill to point out that Wilson is over behind the fence, as always. So holy shit, who was Santa??? Mark stares up at the sky in wonder ...