It was inside a meteorite that fell 20,000 years ago. There seems to be a connection between this Pokémon and the Dynamax phenomenon.
Eternatus is a Poison/Dragon-type Pokémon. It takes double damage from Ice, Ground, Psychic and Dragon, and resists seven types. Its base stats add up to 690: the highest is Special Attack (145) and the lowest is Attack (85).
It does not evolve, and no other Pokémon evolves into it. Its ability is Pressure. It cannot breed: it is in the Undiscovered egg group. In Scarlet and Violet it learns 15 moves by level-up and 40 by TM.
OTHER FORMS
Eternatus Eternamax
Poison / Dragon type, like Eternatus; HP 140 → 255, Attack 85 → 115, Defense 95 → 250, Sp. Atk 145 → 125, Sp. Def 95 → 250; the same abilities as Eternatus.
BASE STATS
ABILITIES
Puts other Pokémon under pressure, causing them to expend more PP to use their moves.
BREEDING
MOVES
WEAKNESSES & RESISTANCES
EVOLUTION LINE
This Pokemon does not evolve