Spectrier is an equine Pokémon with black fur and a purple marking covering the right side of its face extending to the base of its ears. Its left eye is closed with thick, mauve-colored eyelashes. It has a wavy purple mane that transitions into mauve towards the tips, with the tips themselves being translucent. Its fringe and tail are completely mauve. It has slender legs marked with a purple sock pattern. Each of its purple hooves is detached from its legs at the pastern, and the rear pair of the hooves are trailed by spectral mist.
As Spectrier desires isolation and silence, it tends to be active during the night where its energy is heightened. Its nocturnal habits resulted in it having weak eyesight, but its other four senses are keenly sharpened; this allows Spectrier to have an accurate sense of the terrain and location of living things. Its kicks are said to separate a soul from its body, and it can steal the life force of sleeping beings. It feeds on the ambient life-force it steals from others and will attack anyone who would try to disturb it.
Spectrier is known to be very proud and arrogant, preferring to serve individuals it deems the strongest. It once ruled over the Crown Tundra, lording over all the other Pokémon living there and terrorizing humans who intrude on its territory. This lasted until it was defeated and tamed by Calyrex using the Reins of Unity. It has a fondness for carrots, particularly Shaderoot Carrots.
When fused with Calyrex, Spectrier's speed becomes swift to the point it can run a thousand miles within a single day. The strength of Spectrier's spectral power also increases. By Shadow Rider Calyrex's psychic influence, Spectrier can create countless small will-o'-the-wisps. These wisps have the power to steal the opponent's life-force with burning heat. Calyrex can also transform the steed's spectral aura into a black mass. This mass is powerful enough to absorb the life-force and souls of any being's energy like a black hole.
Spectrier debuted at the very end of PASS38. It is revealed it was the former loyal steed of the King Pokémon, Calyrex. In PASS39, Spectrier seeks the Shaderoot Carrot Calyrex grew and after failing to find it, it galloped to Freezington and started causing havoc on the villagers. To protect its people, Calyrex appears to its former steed and powered up by the villagers' belief in its existence, easily blasts Spectrier away, forcing it to flee. In PASS40, Calyrex, Bede, Peonia and Henry, find Spectrier again at the Crown Shrine and as GigantamaxCorviknight and Butterfree appear above the shrine due to the Darkest Day, Calyrex mounts the horse and uses the Reins of Unity to conquer it and both unite into Shadow Ride Calyrex. Spectrier gallops away from the shrine leaving the children to fight by themselves so Calyrex can save the villagers of Freezington, being all saved by Calyrex and Spectrier before they then returned to them, only for Calyrex to faint holding the poisoned Rusted Sword, causing Spectrier to freak out in panic. In PASS41, Spectrier is last seen mounted by Calyrex as it says its goodbyes to Henry and Bede as they leave in a train.
Spectrier and Glastrier are the only Pokémon introduced in the Crown Tundra that were not directly revealed to the public.
Spectrier is the only pure Ghost-type Pokémon to not have an evolutionary relative.
Spectrier together with Glastrier may also be based on the Horsehead Nebula, a horse-shaped nebula near the constellation Orion. This would correspond to Calyrex possibly representing Orion itself (specifically Rigel, its brightest star), or Lepus, the "hare" constellation located right below Orion.
Both Spectrier and its counterpart Glastrier's relationship with Calyrex appears to be based on the legend of Brian Boru and the Pooka. Legend has it that Brian Boru, the High King of Ireland, is the only person to have ever ridden a Pooka, a mischievous faery in the form of a black horse. Brian tamed the Pooka by using a special bridle that contained three hairs from the Pooka's tail and successfully staying on its back through a wild ride. The king then forced the Pooka not to torment Christian people and to never attack an Irishman ever again. This is similar to how Calyrex, a Pokémon known as a king, can only ride its loyal steed, Glastrier or Spectrier, using the Reins of Unity woven in part from hairs from the steed's mane and had to prove itself by riding through the steed's bucking. It also relates to how, in taming this steed, Calyrex stopped the steed Pokémon from tormenting the people of the Crown Tundra. Spectrier in particular may take direct inspiration from the Pooka, being a black horse that mostly appears at night.
Spectrier appears to be based on the Old English Black, an extinct horse breed that influenced the bloodline of modern Shire horses and Clydesdale horses. The ectoplasm around its detached hooves may be a stylization of the feathering of these horse breeds. Its tail shape without noticeable protusion may be a reference to low tail sets, a common conformation found in heavy draft horses. Given its light weight and Speed together with elaborate manes, it is more similar to the Friesian horse, a light draft horse breed favored in jousting and dressage that have also influenced the bloodline of Shire horses.
Spectrier may draw inspiration from legendary horses in Celtic mythology, such as Llamrei, a mare owned by King Arthur in the Welsh tale Culhwch and Olwen. Therefore, its ability to prey on the life energy of sleeping creatures may be a wordplay on 'mare', as both a sleep demon and a female horse, though with different etymology, are spelt as 'mare' in modern English. It may also be based on Dub Sainglend, a black chariot horse owned by the hero Cú Chulainn in the Ulster Cycle of Irish Mythology. It may also take inspiration from other water horses in Celtic and Nordic folklore, particularly Glashtyn in Manx folklore, where it is characterized with reversed hooves in modern renditions.
Alternatively, Spectrier may draw inspiration from the mythological Four Horsemen of the Apocalypse, Spectrier representing the black horse of Famine given its roaming nature and purported ability to absorb life-force from living creatures, or the ashen horse of death, given its Ghost typing and draining of life. It may also be based on the black-colored knight chess piece. Together with Glastrier, it may also be partly inspired by Ema plaques and horse effigies in Shinto shrines that pray for good harvest.
Spectrier may be a combination of spectre and destrier, a type of medieval war horse.
Wraithpos may be a combination of wraith, 霊 rei (spirit), and ἵππος híppos (Greek for horse) or horse.