Gengar

Gengar (ゲンガー Gangar) is a /-type Pokémon, and is the evolved form of Haunter.

Appearance
Gengar is a circle-shaped Pokémon with two large ears and spikes all over its back. Gengar has two red eyes and a sinister smile. It has claws on its hands. Gengar stands on its two legs but it can Levitate too.

Special Abilities
Gengars have the ability Levitate. Levitate makes Gengar immune to -type moves. This Pokémon hides in the shadows. It is said that if Gengar is hiding, it cools the area by nearly 10°F. When there is a Full Moon, this Pokémon likes to scare people by pretending to be their shadow. Then, Gengar laughs at their fear. Gengars are mostly based on being mean and evil by tormenting people and hurting them and overtaking them. It can absorb any surrounding heat, leaving a sudden chill. To steal the life of its target, it slips into the prey's shadow and silently waits for an opportunity. Gengar is also able to merge with and inhabit the shadow of another being.

Origins
Gengar appears to be based off a ghostly cat. Its name is possibly based off doppelganger

Trivia

 * Despite Gengar being able to sneak in shadows, it is unable to learn Shadow Sneak.
 * Despite being part Poison type, it is only able to learn 2 Poison type moves.
 * Gengar is one of the three only stage two Ghost-Type Pokémon. The others being Dusknoir and Chandelure.
 * Unlike most Pokemon, a Shiny Gengar has a small physical difference from a normal Gengar in HeartGold and SoulSilver. In said games, the spikes on a Shiny Gengar's back are shaped differently than a regular Gengar's
 * Gengar is four inches shorter than Haunter, despite it being evolved from Haunter.
 * Gengar and its pre-evolutions are the only Ghost types to have a weakness to -type attacks.
 * No other Pokémon has the same type combination as Gengar and its pre-evolutions.