Necrozma

"You kids... run away... that thing... is a monster!"

- Lusamine to Lillie and the Player about Necrozma. "Lie... Lie... Light!"

- Ultra Necrozma

Necrozma is the main antagonist of the 2017 3DS videogame Pokémon Ultra Sun and Ultra Moon. It is a Psychic-type Legendary Pokémon introduced in Generation VII. It is the mascot Legendary Pokémon of Pokemon Ultra Sun and Ultra Moon, in the forms of Dusk Mane and Dawn Wings Necrozma.

Biology
Necrozma is an entity made out of what appears to be black crystalline material; its large rock-like arms have three claws jutting out of them, as well as a single large whitish crystal protruding from each palm. Small hook-like wings grow out of each of its elbows. Its small legs bend backwards like a bird and have three toes each. It does not seem to use its legs as it can naturally levitate.

The large protrusion attached on top of its head is its tail, which is white in the back with a dark gray symbol resembling a star in the center. The star-like pattern absorbs light that Necrozma can convert into lasers, and shines brightly when it does.

The sides of its head and the top of its tail are covered in spikes, and its face possesses a collection of multicolored shapes, made up of all seven spectrums of the rainbow, which glows white when absorbing light, referred to as its brain prism.

When transformed into its true form, Ultra Necrozma, its appearance takes the form of a large white dragon with four wings and gold armor on its chest, arms, legs, and face. Its eyes take the shapes that formerly made its brain prism, with the right eye having a blue coloring and the left eye having a red coloring.

Necrozma's ability is "Prism Armor", which protects it from super-effective moves by a forth. It gathers light as its energy source, which it can shoot out as its signature move, "Prismatic Laser". Necrozma is known as an incredibly vicious Pokémon, and often fires lasers at anything around it.

Origins
Necrozma was once an entity that spread light across Ultra Space, known as the Blinding One. When it came to Ultra Megalopolis, the people managed to restrain it, imprisoning it in Megalo Tower, using its light as a source of power. While it was captured, Necrozma was tortured by the people, enough that it caused a crippling injury that led to the light within itself to consistently leak out. This causes Necrozma to go berserk, resulting in its desire to drain all light from the universe to regain all the light it lost. After stealing the light from Ultra Megalopolis as it escaped its imprisonment, Necrozma went on a rampage stealing all the light from multiple spots throughout Ultra Space; one of which was the Alola region, where it defeated the guardian deities, but Solgaleo/Lunala managed to defeat it and banish it back into Ultra Space. As its strength kept growing, the Ultra Recon Squad from Ultra Megalopolis explored other worlds to find and stop it before it could become unstoppable.

Sun and Moon
Necrozma was discovered deep underground, where it had been resting for ages, waking from the opening of the Ultra Wormhole. In the post-story, after obtaining every Ultra Beast released into Alola from Ultra Space by Lusamine and Nihilego, Looker mentions a black figure he saw flying around Melemele Island, but shrugs it off since all the Ultra Beasts have been captured. However, visiting Ten Carat Hill will trigger a battle against Necrozma, where the player can either capture or defeat it. It has a 1% chance of appearing, and will respawn instantly should the player flee or knock it out.

Ultra Sun and Ultra Moon
When Lusamine opened the Ultra Wormholes to locate and capture Necrozma, the entity kicked her and Guzma out and began to wreak havoc, but is attacked by Nebby in the form of Solgaleo or Lunala, depending on the player's game. Necrozma manages to defeat Nebby and forcefully merges with it, changing into its Dusk Mane or Dawn Wings form and then battling the player to test its newfound power. After defeating Necrozma, it retreats into Ultra Space.

Afterwards, the player is required by the Ultra Recon Squad to chase after Necrozma on Lunala in Ultra Sun or Solgaleo in Ultra Moon. Upon warping through a white wormhole in Ultra Space, the player is taken to Ultra Megalopolis, where once reaching the top of Megalo Tower, they will find Necrozma reaching its Ultra Burst and becoming Ultra Necrozma, its ultimate form. It will challenge the player and their Pokémon, where all of its stats are boosted by aura.

Upon defeating Ultra Necrozma, it releases Nebby and falls through the floor into another world, without specification on where it went. On the way to the Pokémon League on Mount Lanakila, the player discovers Necrozma in a crater on the mountain, exhausted from its loss of light with a complete loss of memory from traveling through worlds. The player is given the option to share some light from their Z-Ring to Necrozma, and should they accept, Necrozma will become well enough to battle, where the player can be able to capture it. After its defeat, the player will be rewarded the Ultranecrozium Z and obtain the N-Solarizer and N-Lunarizer from Colress to merge Necrozma to Solgaleo or Lunala.

Trivia

 * Despite coming from Ultra Space, Necrozma is not related to the Ultra Beasts; although the International Police have no records of it ever emerging from an Ultra Wormhole, so its classification is still uncertain.
 * Because of this, the Beast Ball is not effective against capturing Necrozma.
 * Necrozma is the 800th Pokémon in the National Pokédex.
 * Necrozma shares its battle theme with Solgaleo and Lunala, even though it shares no connections with the two. This possibly predicted its role in the follow up games from Sun and Moon.
 * Necrozma is the tenth pure Psychic-type Legendary Pokémon, behind Mewtwo, Mew, Deoxys, the lake trio, Cresselia, Cosmog, and Cosmoem.
 * With a catch rate of 255 during its weakened state at the top of Mount Lanakila in Ultra Sun and Moon, Necrozma is the easiest Legendary Pokémon to catch.
 * Initially, in the original Sun and Moon games, Necrozma's catch rate was 3, similar to any other Legendary Pokémon.
 * Necrozma is the first main antagonist in the core series to be a Pokémon itself and not a human.
 * Necrozma is the most evil Pokémon to exist in the game franchise besides Darkrai from the Mystery Dungeon series, this is due to Necrozma having actual intelligence and morality unlike other Pokémon and attempting to steal the light from the universe out of spite for its power being weakened by humans.
 * But unlike Darkrai, Necrozma is also the first Pokémon to be the main antagonist in the core game series.