Character from pokemon-journeys by
The Galarian world-ender -- the infinity-energy Pokémon woken by Chairman Rose, and the crisis behind the Darkest Day event that tests Ash, Goh, and Leon together.
Eternatus is a natural catastrophe with a heartbeat. It arrived on Galar millennia ago, was sealed by the original two heroes of the Darkest Day, and was released by Rose a thousand years too early in his gambit to harvest its energy for future use. When released it does not recognize human concerns; it consumes Dynamax energy across the region, triggers Max Raids in every Gym simultaneously, and begins converting Wyndon's sky into a second storm-front. Its power is mechanically central to the Galar arc: it is the source of Dynamax, the thing every Dynamax Pokémon is unconsciously drawing on. Under pressure it becomes more itself. It is neither evil nor good; it is weather made conscious. It is subdued temporarily by the legendary Zacian and Zamazenta working with the Galar heroes -- an emergency, not a solution, that echoes through the whole final arc.
A massive serpentine Poison/Dragon-type with a skeletal purple-and-white body, a glowing red core in its chest, huge hooked claws, and a crown of sharp spines. In Eternamax form it swells into a cosmic galaxy-serpent the size of a city, radiating Dynamax energy. Moves with writhing, gravity-indifferent menace and roars that rearrange weather patterns.