Near the end of the Main Story, directly before challenging Leon to become the next Galar Region Champion, Chairman Rose will awaken Eternatus, one of the three Legendary Pokemon of The Galar Region, in order to use its power to bring about the Darkest Day. As you deal with Chairman Rose, Leon will actually attempt to defeat Eternatus. After subduing Eternatus, Leon will attempt to capture it.
But after breaking out of the Poke Ball, Eternatus will be too much for Leon to handle. It will then be up to your character to battle Eternatus, a dual Poison / Dragon Type Pokemon, but it won't be able to be captured during this Encounter. It will be at Level 60, knowing the moves Cross Poison, Dragon Pulse, Flamethrower, and Dynamax Cannon.
After defeating it in battle, Eternatus will absorb enough energy to Dynamax, officially changing into its Eternamax Form. When in this form, Eternatus has the highest Base Stats in the entire World of Pokemon. Because of this, it must be faced in a Max Raid Battle. Hop will immediately team up with your character to battle Eternamaxed Eternatus, but your Pokemon Attacks will do nothing to Eternatus for the first three moves of the Raid Battle. It is then that Hop suggests using the Rusty Sword and Rusty Shield, and after both of you bring them out, Zacian and Zamazenta appear. The two Cover Legends will then team with you and Hop in order to take down Eternatus.
When in its Eternamax Form, Eternatus will remain a Poison/ Dragon Type Pokemon. It will also continue to be at Level 60, still knowing the moves Cross Poison, Dragon Pulse, Flamethrower and Dynamax Cannon. But, as mentioned, Eternatus will receive an astonishing 435 Point Boost to its Base Stats Total when in its Eternamax Form. It will take the help of Hop and both Cover Legends to defeat Eternamaxed Eternatus, but after it has been defeated, you will earn the chance to capture it.
Want to know if Eternatus can change forms outside of its Capture Battle? Click Here to see if it can!
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