

After Twilight Sparkle's capture, the Storm King appears before her and uses the Staff of Sacanas to drain her and the other princesses' magic, granting him massive power and control over the sun and moon.

Later in the film, Princess Skystar reveals that she, her mother Queen Novo, and the rest of the seaponies used to be Hippogriffs and live atop Mount Aris before the Storm King invaded and forced them to flee underwater. In his first on-screen appearance, the Storm King communicates with Tempest via potion spell, and he reminds her of the terms of their agreement: deliver to him the princesses' magic and empower his Staff of Sacanas in exchange for restoring her broken horn. His second-in-command Tempest Shadow, underling Grubber, and army of Storm Creatures are sent to Canterlot as an advance force to occupy the city and secure the magic of the four Alicorn princesses. The Storm King appears in My Little Pony The Movie as the central antagonist.
