In the spin-off game Pokémon Ultra Fire Red XD, Unjoy has a Mega Evolution. The backsprite of it glitches even further, resembling Gigyas. Its canonicity is debatable however, as the events of the game take place inside of Kanye's mind.
Unjoy has the highest base HP stat of all Pokémon and the highest base Special Defense stat of all non-legendary Ghost-type Pokémon.
Its cry is a remix of the Lavender Town theme.
Its stats are identical to Blissey's, similar to how Hanginy and Chancer's stats are identical to that of Happiny and Chansey respectively.
Unjoy is the only member of its line to not resemble a member of the Chansey evolutionary family.
In the original concept art, Unjoy had white, Haunter-esque hands. This was lost in translation when it was redrawn, becoming ghostly flames in its hair loops instead.
Its footprint is a glitchy square that says "HELP ME".
Unjoy’s backsprite is glitched. This could be because of something...
Its shiny is a reference to Officer Jenny.
Unjoy is based on the decapitated head of Nurse Joy, a character originating from the Pokémon anime. Its shiny form is based on Officer Jenny, who also comes from the anime. Both of these characters have multiples of themselves running around, but neither are a single entity. Additionally, it may be a reference to cliche Pokemon creepypastas, specifically the many pastas involving Nurse Joy/the Pokémon Center nurses.
It could also be based on ebola chan, but that's unlikely
Unjoy could also have took inspiration from the Mythical creature, the Krasue.
Unjoy literally means "not joy" or undead and joy referring to nurse joy in the Pokemon anime.