The Marvel Cinematic Universe's Black Widow has a subtle anachronism in the form of a toy that the young Yelena clutches in the flashback at the beginning of the film.
A fan with the username chesterforbes pointed out the error in a post on Reddit, saying, "When young Natasha and family arrive in Cuba and are taken away, Red Guardian is seen holding a doll that Yelena brought with her. That doll was a Twilight Sparkle doll from My Little Pony: Friendship is Magic which ran from 2010-2020." The scene in question, which sets the stage for Natasha and Yelena's relationship as adoptive siblings in a family of spies, is set in 1995.
My Little Pony is a Hasbro franchise which began in the 1980s with a set of collectible plastic pony figures. The popularity of the toys led to multiple cartoon series and movies, but with each reboot, the design of the ponies changed and different individual characters were featured.
The 2010 My Little Pony: Friendship Is Magic cartoon was a cultural phenomenon which drew many adult fans in addition to its target audience of young girls. The lead character was Twilight Sparkle, a purple and pink unicorn who eventually became a winged alicorn and the Princess of Friendship. Toys modeled after Twilight Sparkle have a different shape from the earlier My Little Pony toys, so the one used as a prop in Black Widow is fairly recognizable to those who are familiar with the character.
The Reddit post goes on to correctly state, "Thus that doll should not exist in the 90s. Hell it shouldn’t even exist during the first Iron Man movie."
They also made sure to direct the credit for the observation to a fan of a different kind: "I would like to credit my 7 year old daughter who’s watched My Little Pony more times than I can count and has so many of the toys for me ever even noticing this."
My Little Pony: Friendship Is Magic came to its end after an impressive nine seasons, giving way to a new incarnation of the franchise through the CG-animated movie My Little Pony: A New Generation, now streaming on Netflix,
Black Widow, starring Scarlett Johansson, is the first and only MCU movie focused on the founding Avenger Natasha Romanov, released after the character's death in Avengers: Endgame but set in the past to illuminate an untold period of her life between other films in the franchise.