Necrozma's body appears to be constructed out of black crystalline material; its disproportionately large arms have three claws jutting out of them, as well as a single large whitish crystal protruding backwards from each arm. Its small legs bend backwards like a bird's and have three toes each. A single small, hook-like wing grows out of each of its shoulders. The large protrusion attached to its head is its tail, which is white in the back with a dark gray symbol resembling a star in the center. This part of the tail glows while absorbing light that it converts to lasers. The sides of its head and the top of its tail are covered in spikes. Its face is actually a prism-like object known as the brain prism, which possesses a collection of multicolored shapes that resemble eyes. Despite being pitch-black, Necrozma's body constantly refracts light like a prism.
Necrozma can take control of Solgaleo or Lunala by fusing with them, allowing it to assume its Dusk Mane Necrozma or Dawn Wings Necrozma forms, respectively. Because Necrozma is forcibly absorbing their light, Solgaleo and Lunala constantly glow in a manner similar to their Radiant Sun and Full Moon phases while fused. In both cases, the hosts' bodies are covered in parts of Necrozma's body, which are arranged like armor; in particular, Necrozma's large clawed arms are prominent in both forms, though they lack the large crystals jutting from them. Both forms have a triangular helmet with Necrozma's brain prism prominently visible, with bright glowing blue eyes for Dusk Mane Necrozma and pink eyes for Dawn Wings Necrozma. Using the split tail on Dusk Mane Necrozma's sides or Dawn Wings Necrozma's back, both of these forms can propel themselves forward using black light.
Once it absorbs enough light, Necrozma can undergo a process called Ultra Burst to reclaim its true form: Ultra Necrozma, a colossal, shining dragon armored by pieces of Necrozma's original form. Most of its body is made of pure light energy, as indicated by its non-solid shape; this light is produced from the brain prism, which is no longer visible. Ultra Necrozma has two pairs of clawed wings, a long, spiked tail, and a head resembling a shining star with several long horns on the sides and top. Its face is armored and has multicolored heterochromic eyes; the left eye is primarily red, while the right is mainly blue. In this form, Necrozma's large clawed arms and small legs have swapped places, respectively becoming Ultra Necrozma's feet and parts of its wings. As Ultra Necrozma, all of the pieces of Necrozma's base form have now become a shining golden color, though it will return to black if the light it has stolen escapes. Ultra Necrozma has a body temperature of 10,000 degrees Fahrenheit; anything that it touches will melt from the extreme heat. It can fire laser beams from every part of its body, and these lasers can reach over 18 miles away, burning through everything in their path. As seen in the anime, when Necrozma uses up all its light it enters into a deep slumber unless it absorbs more light.
Necrozma originates from Ultra Space and is capable of opening and traveling through Ultra Wormholes. In Ultra Megalopolis, it is known as the "Blinding One" (Japanese: かがやきさまRadiant One). It once had the ability to give light, but lost this ability after being injured under unknown circumstances; Professor Kukui and Lillie theorize that the Sparkling Stones used to perform Z-Moves are fragments of Necrozma's body that it lost upon this injury. In its incomplete state, Necrozma suffers constant pain and displays immense hostility. In an effort to restore itself to its original state, Necrozma steals light from other places and beings, including Solgaleo, Lunala, and Ultra Megalopolis; this behavior caused it to be feared as the "pillager of light" in ancient Alola. When Necrozma absorbs light from a world, that world becomes shrouded in darkness until the stolen light is returned. While absorbing light, Necrozma's brain prism glows white.
Ultra Necrozma debuted in Tough Guy Trials!, during a fantasy. Acerola showed Ash a book containing a legend detailing the origins of Alola, in which Ultra Necrozma, Solgaleo, and Lunala first brought light to the region. The ancient people dubbed Necrozma, who shined the brightest out of all three, the "Blinding One". Team Rocket also heard the story and contacted Giovanni about it, only to find out from Matori that he already knew of Necrozma and ended the transmission, much to their surprise.
A black or white abbreviation in a colored box indicates that Necrozma can be tutored the move in that game
A colored abbreviation in a white box indicates that Necrozma cannot be tutored the move in that game
Bold indicates a move that gets STAB when used by Necrozma
Italic indicates a move that gets STAB only when used by an evolution or alternate form of Necrozma
When Necrozma is fused, it tries to learn a new move in the same way that other Pokémon may learn new moves upon evolving. If Necrozma changes to its normal form, it immediately forgets the special move of the form it was in (if it still knows it); if the only move that Necrozma knows is the form's special move, then that move will be replaced with Confusion.
Necrozma has the most body styles of all Pokémon with a total of four between its different forms.
Necrozma's status as an Ultra Beast is unclear. While it is not referred to as an Ultra Beast in the games, it, alongside the other members of the Light trio and their pre-evolved forms, are referred to as such in the anime. Necrozma is also given the codename of UB Black (Japanese: ＵＢ:ＢＬＡＣＫUB: Black) in the anime like the other Ultra Beasts. Additionally, Dusk Mane, Dawn Wings, and Ultra Necrozma are classified as Ultra Beasts in the TCG, while its base form is not.
Necrozma is fought three times in the main story of a core series game, more than any other Legendary Pokémon.
Necrozma has access to the most exclusive Z-Crystals with a total of three.
As seen in the climax of Pokémon Ultra Sun and Ultra Moon, as well as in Full Moon and Many Arms!, Necrozma is able to fuse with Solgaleo and Lunala without the need for N-Solarizer or N-Lunarizer.
Necrozma's Dusk Mane and Dawn Wings forms may be based on the concept of solar and lunar eclipses, respectively. The forms' alternate names in Japanese, 日食 nisshoku (solar eclipse) and 月食 gesshoku (lunar eclipse) can also be literally translated as "eating the sun/moon", reflecting how Necrozma absorbs Solgaleo or Lunala to assume those forms. Its Ultra Necrozma form may be based on giant stars or supernovae. Design-wise, Dusk Mane Necrozma and Dawn Wings Necrozma retain Solgaleo's lion and Lunala's bat bases, respectively, while Ultra Necrozma resembles a four-winged wyvern. The fact that Necrozma transforms into a Dragon-type could be based on legends about Kihawahine, a Hawaiian dragon goddess.
Necrozma may be a combination of νεκρός nekrós (Ancient Greek for dead), 黒 kuro (black), and πρῖσμα prîsma (Ancient Greek for prism). It may also involve Project Ozma, an experiment made to search for extraterrestrial life.