In Godzilla: King of the Monsters, Mothra joined forces with the titular Titan to help battle Ghidorah. Unfortunately, she was severely wounded during the fight and, using the last of her strength, embarked on one final attack which saw the fan-favourite monster burn up and disintegrate.
However, as her ashes fell on Godzilla, he was able to unlock his "Burning Godzilla" form and annihilated Ghidorah with a series of thermonuclear pulses (the first of which took on the appearance of Mothra's wings).
A newspaper article later suggested that an egg suspected to be that of Mothra had been found, and Godzilla x Kong: The New Empire finally brings her back from the dead!
In the movie, we watch as the human characters take former Skull Island inhabitant Jai into Hollow Earth. It's revealed that she's not really the last of her people, as they've taken refuge deep beneath the surface and live behind a barrier that keeps them safe from the evil Skar King.
Jai discovers she's a conduit destined to speak with and awaken Hollow Earth's guardian, and it's Mothra who subsequently emerges from inside a massive chrysalis. Her survival is never explained, but looking at Godzilla franchise lore, we can safely assume she rebirthed herself in that egg as it's how the fan-favourite has cheated death on multiple occasions.
Mothra doesn't get a huge amount of screentime in Godzilla x Kong: The New Empire but the "Queen of the Monsters" as she's described here plays a pivotal role in the eventual defeat of the Skar King.
The Titan is crucial in uniting Godzilla and Kong and holds back the villain's forces when the Titan frenemies deal with their newfound foe once and for all. As the movie ends, we're left to assume Mothra returns to Hollow Earth to continue watching over Jai and her people.
The epic battle continues! Legendary Pictures' cinematic Monsterverse follows up the explosive showdown of 'Godzilla vs. Kong' with an all-new adventure that pits the almighty Kong and the fearsome Godzilla against a colossal undiscovered threat hidden within our world, challenging their very existence—and our own. 'Godzilla x Kong: The New Empire' delves further into the histories of these Titans and their origins, as well as the mysteries of Skull Island and beyond, while uncovering the mythic battle that helped forge these extraordinary beings and tied them to humankind forever.
Godzilla x Kong: The New Empire stars returning Godzilla vs. Kong actors Rebecca Hall, Brian Tyree Henry, and Kaylee Hottle alongside Dan Stevens (Legion), Alex Ferns (The Batman), and Fala Chen (Shang Chi and the Legend of the Ten Rings).
The screenplay is by Terry Rossio (Godzilla vs. Kong) and Simon Barrett (You’re Next) and Jeremy Slater (Moon Knight), from a story by Rossio & Wingard & Barrett, based on the character "Godzilla" owned and created by TOHO Co., Ltd.
Godzilla x Kong: The New Empire is now playing in theaters.