Missing Episode/Advertising

Despite not being considered TV episodes, advertisements are the #1 victims of this Trope. There are many reasons for advertisement pulling, most notably public outrage. Fortunately some missing advertisements have survived over the years through VHS tapes and recordings, and as a result they are widely shown throughout the internet. Otherwise, you're out of luck if you miss your favorite Advertisement and want to see it again.
Effective January 2, 1971, the FCC called all tobacco companies to remove their commercials advertising their cigarette, cigar, or tobacco products and ordered them to never be shown on TV again. Instead, ads made opposing cigarette use were made, and they continue to this day. As for the tobacco ads, only certain numbers of them (most notably the Flintstones Winston cigarettes ads) are widely available on the Internet, and others may be lost forever.
A Burger King commercial featured a scientist chasing the King himself and shouting out "Stop that King. He's crazy!". It was pulled following legal threats by various mental healthcare groups, and hasn't aired since then.
- Supposedly, McDonald's may have also shared displeasure with the ad, but that was for a completely different reason (possibly the price it advertised in the commercial).
If you're a fan of Rick and Morty you probably know that the eponymous duo has appeared in a lot of commercials, for such brands as Old Spice, Carl's Junior, and Wendy's, but they also made a series of them for Subway that will likely never be seen again. Supposedly, these ads also featured the franchise's disgraced pitchman Jared Fogle, and were completed mere weeks before his arrest on charges of child pornography and molestation. For obvious reasons, the series was cancelled.