Rockruff evolves into Midday Form Lycanroc when leveled up during the day (in Generation VII, in Pokémon Sun and Ultra Sun only).
Rockruff evolves into Midnight Form Lycanroc when leveled up at night (in Generation VII, in Pokémon Moon and Ultra Moon only).
A Rockruff with Own Tempo evolves into Dusk Form Lycanroc when leveled up from 7 PM to 7:59 PM in real-time (Generation VIII) or 5 PM to 5:59 PM in in-game time (Pokémon Ultra Sun and Moon, equating to 5 PM to 5:59 PM in real-time for Ultra Sun and 5 AM to 5:59 AM in real-time for Ultra Moon).
Lycanroc is a canine Pokémon resembling a wolf. It has three possible forms: Midday Form, Midnight Form, and Dusk Form. The first two forms are influenced by Solgaleo and Lunala when bathed in solar or lunar energy. The third form is said to have been influenced by the setting sun of the evening.
In its Midday Form, Lycanroc resembles a quadrupedal, light brown wolf. It has a white underbelly that extends up around its muzzle and eyes in a mask-like marking. It has pointed ears with dark brown tips and pink insides, big blue eyes, and a triangular, dark brown nose. There are four sharp fangs in its mouth: two in the upper jaw and two in the lower. Large tufts of brown fur extend from the sides of its head; three tufts on each side. A bushy, white mane covers its neck. Four dark brown rocks poke out of its mane, creating a shape similar to a stylized sun. The rocks are said to be razor-sharp. The lower portions of this form's legs are white, and each foot has three dark brown claws. It also has a long, fluffy white tail.
In its Midnight Form, Lycanroc instead resembles a slouched, bipedal wolf or werewolf. It has short red fur with white on its lower legs and a white streak that covers its face, underbelly, and tail. It has pointed, button ears with black tips, three large tufts of fur on each side of its face, a triangular black nose, and a mouth full of sharp teeth. While the sclerae, irises, and pupils of its eye are visible, they all glow a pinkish red and no distinctive colors are visible. A mane of fur covers its back and shoulders, sweeping forward over its head to form a crescent moon shape. On either side of its body, just below the shoulders, two small rocks resembling claws poke out of the mane. A single, bigger stone projects out of the front of the mane over its head. Each of this form's paws has three black claws, and it has a stubby tail covered in long fur.
In its Dusk Form, Lycranroc resembles a combination of its Midday and Midnight Forms. The body is similar to Midday Form with the same white color except with orange-gold fur. It retains the three brown claws for all four feet. The white fluffy mane resembles a sun with part of the crescent moon. It also has four rocks around its neck like a sun as well along with a single, bigger stone coming from the mane over its head. The face resembles Midday Form but is orange-gold with bright green eyes, the eyes can change to bright glowing red when angry or attacking.
The Midday Form has a calm and cautious personality. In order to avoid needless fighting, the Midday Form prefers to live alone and does not form a pack with others of its kind. However, it is a fiercely loyal partner to Trainers that accept it during its unruly stage. In battle, it darts past opponents while attacking them with the rocks in its mane. These swift movements leave many foes bewildered and backed into a corner. It always aims for the foes' weak spot using its fangs. Broken fragments of its stone mane are considered good luck.
In contrast, Lycanroc's Midnight Form is thrilled by battling and becomes more excited the stronger its opponent. This excitement is what causes its eyes to glow.  The Midnight Form is known to be reckless. Its strategy consists of closing in on its opponent and encouraging attack, then countering with a powerful blow that knocks out its opponent. The full force of its headbutts can destroy giant boulders. Trainers that can draw out its power earn its trust, but it despises those that it disagrees with or who try to force it to fight.
The Dusk Form Lycanroc shares traits from the previous two forms. Its stance, calm demeanor, and loyal nature are shared with the Midday Form. However, it also shares the Midnight Form's fighting spirit, including the red, glowing eyes at the moment of attack. Due to only evolving at sunset, the Dusk Form is considered the rarest of the three forms.  The Dusk Form of Lycanroc is rather difficult to train due to its temperamental nature.
A Midnight Form Lycanroc appeared in I Choose You!, under the ownership of Cross. It first appeared when Cross encountered Ash, Verity, and Cross's former Charmander. Later on, Lycanroc was among the Pokémon subjected to the control of Marshadow, but it managed to break free when Cross reminded it of how they first met.
Rockruff, the Puppy Pokémon. A Rock type. Rockruff have lived with humans since ancient times. They train themselves by running around. Rockruff evolves into Lycanroc, which has two different forms based on when it evolves. It evolves into Midday Form Lycanroc during the day and Midnight Form Lycanroc during the night. Furthermore, when it gets close to evolving, Rockruff's temperament becomes more aggressive, and it tends to act more independent. It's common for it to disappear and then return after it has evolved.
Akira's Rockruff has the unique ability to evolve into Lycanroc and then devolve into Rockruff again, thanks to the strange red stone on its neck. It also has the ability to change in between its Midday and Midnight Forms while being evolved.
The QR Code displayed in the Pokédex entry for Dusk Form Lycanroc is actually that of Midday Form Lycanroc.
Lycanroc and Mr. Mime are the only two Pokémon known to have 6 possible abilities between their forms, the most of any Pokémon.
Overall Lycanroc shares traits with the extinct Japanese and Hokkaido wolves in particular. Its Rock typing seems to be a reference to the link between wolves (also called as 山犬 yamainu, lit. mountain dog) and mountains in Japan.
Lycanroc's Midday and Dusk Forms appear to be based on a wolf, while its Midnight Form appears to be based on a werewolf. The duality between Midday and Midnight Forms may be a reference to the okuri-inu, a mountain wolf creature that could take either a protective approach, similar to Midday Form's behavior; or an aggressive one much like Midnight Form's.