Gengar

Gengar is a dark purple, bipedal Pokémon with a roundish body. It has red eyes, a wide mouth that is usually curled into a sinister grin, and pointed ears. On its back are numerous spikes, and it has smaller spikes on top of its head similar to tufty fur. Its arms and legs are short with three digits on both its hands and feet. It also has a stubby tail.

Gengar has the ability to hide perfectly in the shadow of any object, granting it exceptional stealth. Its body acts as a heat sink, cooling the temperature of the surrounding area by nearly 10 °F (5 °C) by absorbing its warmth. It is shown in Pokémon the Series that Gengar can fly, turn intangible, possess people and other Pokémon, create illusions, pass through dimensions, and extend its tongue by several meters. In certain media, such as POKÉMON Detective Pikachu and the Pokémon Ranger series, it is also able to create copies of itself. Gengar is very mischievous, and at times, malicious. It enjoys playing practical jokes and casting curses, such as pretending to be one's shadow during a full moon, then behaving erratically, or attacking people who get lost in the mountains. When the quarry notices, Gengar takes delight in its victim's terror. However, it has been known to be loyal to a Trainer who treats it well. It waits in people's shadows or the dark areas of their homes before stealing their life force. This is because it was once a human and wishes for a traveling companion. Being the result of Evolution via trading, Gengar is rarely found in the wild, though they can be found in caves and dark places where shadows form. As mentioned in Pokémon Sleep, Gengar is known to sleep deeply while hiding in the shadow of a target it plans to curse.

Forms

Gengar has two forms: Mega Gengar and Gigantamax Gengar.

Mega Gengar

As Mega Gengar, a portion of its body sinks into the ground, and its arms and tail lengthen. The lower portions turn a more reddish-purple, and a third eye appears on its forehead. This new unblinking eye is oval, yellow, and allows it to see into other dimensions. The spikes on Mega Gengar's back are more numerous and pointed, and additional spikes appear on its hands and tail. Its ears are now considerably longer and tilt backward.

Mega Gengar has the ability to access other dimensions and has a vicious nature. It has no interest in opponents unless perceived as prey, and its relationships are warped due to Mega Evolution. Mega Gengar desires to take and curse the life of anyone or anything in its path; it may even curse its own Trainer. It sinks into another dimension to wait for a chance to attack; this power allows it to appear anywhere it wants to be. Mega Gengar caused an incident one time where it had one of its legs stick out of a wall.

Gigantamax Gengar

As Gigantamax Gengar, it becomes larger, with portions of its body sinking into the ground, and only the head, tail, and arms remain. Its body changes from dark-purple to light-purple, and its eyes become white with yellow sclera. The inside of its mouth changes to resemble a tunnel with a long purple tongue sticking out. Three red clouds surround the top of Gengar's head.

Gigantamax Gengar's mouth is rumored to not lead into its body, but the afterlife instead due to its cursed energy. By laying a trap, it attempts to steal the lives of those it captures. Should someone stand near its mouth, they can hear the voices of their loved ones calling out to them.

Evolution

Gengar evolves from Haunter and is the final form of Gastly.

(Source: Bulbapedia)