It’s been rumored for a very long time, but now it looks more and mor likely to be happening. One of the most infamous monsters in the Marvel Universe will soon be making their MCU debut in Shang-Chi and the Legend of the Ten Rings.
According to Daniel Richtman (via Full Circle Cinema) Fin Fang Foom will indeed be appearing in Shang-Chi. An older 4Chan plot leak from months ago, which has been spread around Reddit, was the first to say the alien dragon would appear and that the Mandarin makes Shang-Chi participate a fight tournament to earn the rings. It’s sounding more likely that plot leak has some elements that are accurate.
There have been sly hints to Fin Fang Foom in the past movies of the MCU, specifically the Iron Man trilogy. In the first Iron Man, an Adi Granov poster of his Fin Fang Foom design can be seen on a building during the night-time freeway scenes, and of course in Iron Man 3 people thought the dragon carving behind Trevor on the movie posters was a nod to the alien dragon.
With the MCU going full cosmic now and people used to shapeshifting aliens with the Skrulls, giant celestial beings, and purple conquerers who wipe out half the life in the universe, a giant shape-shifting alien dragon isn’t out of the question for the movies.