What's scarier than ghosts and demons on Halloween? Statistics and quantum theory! *horrified shriek*

Full credit to Tempestryder for Purradox's idea - finally got around to drawing it!

Purradox, the superposition pokemon
Purradox is a small dark-and-ghost type pokemon sometimes found in the urban areas of the Osai region, though many people are firmly convinced it's an urban legend. Purradox seems to be a pokemon similar to purrloin, a cat-like pokemon from Unova, but attempts to study it have met with failure - under bright light it seems to be nothing more than an empty cardboard box. When it isn't being directly observed, or in conditions of dim lighting or poorer, the box meows and moves around on its own. Supposedly the first purradox was created by an unethical scientist studying quantum theory on living pokemon. Purradox evolves at level 30, either into purrabolic during the night, or into purrfidy during the day.

Purrabolic, the decay-state pokemon
Purrabolic is a medium-sized ghost-type pokemon from the dark alleys and graveyards of urban Osai. It has a prankish, tricky nature that can become malevolent if its trainer is cruel - it will not stand for being mistreated. It can disappear and reappear at will, often appearing grin-first. Places haunted by a purrabolic can take on its sickly green glow over time, and often attract other ghost-type pokemon. Keeping it in its pokeball seems to greatly diminish this effect.

Purrfidy, the stable-state pokemon
Purrfidy is a medium-sized dark-type pokemon from urban areas of the Osai region. On the surface there is nothing wrong with this pokemon, it seems normal and healthy in all respects. However it seems to exude an undefinable aura of "wrongness", as though something happened to it during evolution that caused it to become somehow far more sinister. Perhaps because it always seems to be watching its trainer, never blinking, always grinning. Even within its pokeball, the sense of being watched never really goes away.