A Dark Memory being installed into the disk drive in Silvally's head in the anime
Silvally is a quadruped, chimeric Pokémon with traits from a variety of creatures. It has a mammalian head with mechanical parts. Covering most of its head and neck is a thick, silver mane that extends down over its chest. Its blunt snout is metallic on the bridge of its nose and upper jaw. It has a triangular black nose framed by three red lines, pointed ears with bright pink and black insides, one visible fang on each side of its lower jaw, and a slight overbite. Its eyes are bright silver, have no visible pupils, and appear to be surrounded by an empty, black space. On each side of its head is a circular, metallic drive, with a white circle crossed by a metal line. On top of its head is a large, axe-like fur or feather crest. The tip of the crest as a hooked, metallic piece, while the back has three white feathers.
Silvally's lower body is mostly covered in short, black fur. The lower half of each front leg is insectoid and green with spikes along the back, while the rear legs have thick purple scales on the flanks, shins, and on the top of the foot. All four of its feet have three toes, but in the front two toes face forward and one backward. Additionally, the hind paws have a short, purple claw on the back of the ankle. Its fish-like tail consists of two dark blue spines with a white fin stretched between them. The top spine has a line of short, gray spikes.
Once it finds a partner it trusts, Type: Null destroys its own control mask to become Silvally. It reverts to its natural, wild temperament, but it is nonetheless loyal to its Trainer, and will even risk its own life in its partner's defense. The destruction of its mask re-activates its RKS System, allowing it to change its type according to the memory attached to it; its eyes, spikes, drives, and fin membrane all change color to match its current type.
Silvally, like its pre-evolution Type: Null, seems to be based on a chimera. Parts of it also resemble a griffin. Silvally's concept also bears resemblance to Arceus. Like its pre-evolution, it also appears to be based on Frankenstein's monster due to the bolt-like objects on its face and it being created from cells of different Pokémon types.
Silvally may be a combination of silver and ally. In-universe, it was named by Gladion.