Dusk Mane Necrozma Battle

Walkthrough: After fusing with Nebby and turning into its Dusk Mane Form, you will be forced into battling Necrozma. In this altered form, Necrozma will be at Level 50 and have the moves of Sunsteel Strike, Morning Sun, Psycho Cut, and Night Slash. It will continue to have Solgaleo's Psychic / Steel Typing, but will keep its Prism Armor Ability.

After defeating Dusk Mane Necrozma, it will flee back into Ultra Space (still in this new form) and back to Ultra Megalopolis. After it does, Ultra Beasts will be released into Alola Region, forcing the Island Kahuna's (as well as Hau) to help defend the region. As all of this happens, a darkness will appear all over The Alola Region, as Necrozma has stolen the light of the Alola Region in the form of the Legendary Pokemon.

After it flees back into Ultra Space, the Ultra Recon Squad will appear. Since your character has the power of light through your Z-Ring and Z-Crystals, they believe oyu may have what it takes to defeat Necrozma and save Solgaleo. They then permit you the use of their Legendary Pokemon, Lunala, to travel back through Ultra Space to Ultra Megalopolis. You will then have to do this, finding a White Wormhole in Ultra Space to reach said location.