It is related to BUNEARY, but is much more crafty. It conceals itself using trickery, so many people don't believe it exists.
Jackdeary is a bipedal pink rabbit-like Pokémon with a yellow stomach, muzzle, and paws. A pair of small purple antlers sprout from its head. It has white fleece-like fluff on its neck and the tips of its long ears. Its tail is long and white and appears to have the same fluffy texture.
Jackdeary is crafty and uses its wit primarily to avoid detection. Its ability to learn moves such as Feint, Confuse Ray, and Baby Doll Eyes are examples of this wit as applied to battling.
According to its Pokédex entry, Jackdeary is a trickster Pokémon that often conceals itself using ruses and tricks. Due to its method of evolution, it can be assumed that Jackdeary has some affinity for alcohol, most likely relating to its basis on the jackalope creature, which is said to enjoy drinking alcohol.
Jackdeary can be found in Route 13. Because of their similarities to rabbits, it's possible that they may burrow in the route's tall grass.
Jackdeary's current cry is very similar to Buneary's cry, perhaps as an homage, since the two share many parallels including Jackdeary's shiny sprite sharing a color pallet with Buneary.
An Easter-themed Jackdeary was given out over Mystery Gift for the Easter of 2017. Easter Jackdeary always have the Pixilate ability.
Jackdeary is the only Pokémon in the game whose catch rate actually increases when it evolves, despite its evolved form not being possible to catch in the wild.
Jackdeary is based on a Jackalope, a creature from North American folklore that was popularized by a taxidermist grafting deer antlers onto a rabbit. Jackalopes are said to be tricksters and enjoy sugar and alcohol. It could also be based on the Ometochtli from Aztec mythology, which could explain its alcoholic theme as well as the location of the region.
Jackdeary comes from jackalope and deer. Its name also references the official Pokémon Buneary and is a pun on Jack Daniel's, a type of whiskey.