Haunter

Haunter, the Gas Pokémon, is a Ghost/Poison-type introduced in Generation I. It evolves from Gastly starting at level 25 and evolves into Gengar when traded. Haunter is known for its mischievous and eerie nature, often depicted floating through dark places, lurking in shadows, and playing pranks on unsuspecting humans. Its Pokédex entries consistently describe it as a gaseous being that can pass through walls and enjoys scaring people, sometimes to the point of draining their life force. In the anime, Haunter is famously associated with the Lavender Town arc and Ash's temporary companion, a Haunter that preferred humor over malice. In the games, it's a staple of Ghost-type teams and a challenging opponent in haunted towers and mansions. Its unique evolution method through trading has made it a memorable part of the Pokémon experience, encouraging player interaction. As a Ghost-type, Haunter is strong against Psychic and Ghost types but vulnerable to Dark and Ghost attacks, and immune to Normal and Fighting moves, reflecting its ethereal form. Its role as the middle evolution in a popular and powerful evolutionary line contributes to its enduring cultural significance among fans.