There was a time in Magic: The Gathering where opening a pack meant you would likely get a useless ad card.
For roughly 17 years, between 2007 and 2024, Magic booster packs always seemed to come with a card that no one was ever excited about: marketing cards. These were cards specially printed to promote something Magic related. Early ones, like Tenth Edition boosters, promoted the Magic website and this strange new thing called Facebook to join them there.
And there was a reason for this - the 16th card was in there because the marketing team found that this as the only way to reach some players, especially more casual players, about things happening in Magic.
R&D was also interested in this because each new block had new mechanics and rule updates, and they needed a non-internet way to keep players informed. So it was halfsies - one side promoting a Magic thing like online or an upcoming set, and half more game explanation. For some, they could also be half token or half stand-in, to increase the liklihood players keep or use them.

Players were not happy either, with many drafts and deck building aftermaths always having a cluster of them ready to be thrown away. Only the most completionist players bothered to keep any. Still, Wizards of the Coast kept printing them out, despite the online presence of the game quickly expanding and players having multiple outlets, like the MTG reddit page, to quickly find out about upcoming things. This led to fewer marketing cards to be included over time, with a reduction occuring starting with Battle for Zendikar in 2015, and them being reduced to having to almost always be paired with a token side by Murders at Karlov Manor in 2024.

Most were pretty standard, directing players to visit the website, a social media page, or check out Magic: The Gathering Online. However, the heyday for these cards was between 2007 and 2015, so it makes sense. But other marketing cards went a bit further, being blatant advertisements. Like in 2011 with the Disney movie The Sorcerer's Apprentice where Magic played a small part.
They used cards to heavily promote the film in the Scars of Mirrodin block.

However, marketing cards were virtually non-existant by late 2024, the Duskmourn being the last expansion to include them. By the time Aetherdrift came out a few months later in early 2025, Wizards had axed the cards. And its pretty obvious why - even casual fans can now find all the latest updates anywhere from Reddit to the site to Magic influencers, to YouTubers online. You also don't need cards to help explain the rules of commander anymore since those can be quickly looked up via smartphone, laptop, or tablet.

Nonetheless, the cards still pop up thanks to older packs being opened up and the popularity of chaos drafts. But, for the future, these cards will never be in another booster pack.
Probably.