Haunter

Haunter is a Ghost, Poison-type Pokémon from the Kanto region. It evolves from Gastly after being fed 25 candies and evolves into Gengar when fed 100 candies or with no candy cost if traded.

Trivia

 * During the Halloween event in 2017, there were shiny forms of Gastly family members added to game data, although they weren't released to be caught in gameplay.