Mt. Lanakila Necrozma .

After being weakened by the grand battle at Megalo Tower, Necrozma returns to Alola.
During this battle, Necrozma can be caught at Mount Lanakila, before the Elite Four.

After the capture, the player will pick-up Ultranecrozium Z, and Colress will appear to give the N-Solarizer and N-Lunarizer Key items.
This encounter cannot be shiny. Details below refer specifically to this file.

Species   Necrozma   Nickname   (default, in )   OT   PPorg   TID   171117   Distribution   In-Game Encounter   Location   Mount Lanakila   Dates   Nov 18, 2017   PID   Cannot Be Shiny   Games   UM

Lv. 65

Nature   Adamant   Ability   Prism Armor (1)   Item   Ultranecrozium Z

Moves   (ITALIC means Relearnable)   Photon Geyser   Iron Defense   Power Gem   Night Slash

Format Ver.1.0.5-5, Post Updated Date:20171115_1724