Black Fog is an alternate evolution to Haunter which appears once in the manga, and once in the anime (where it simply referred to itself as Ghost). It is also referred to as Giant Haunter.
Black Fog appears as a Giant Haunter, in the manga it appears with a much spikier appearance than regular Haunter and it's claws and teeth appear sharper. In the anime it has red glowing eyes.
As stated in the Electric Tale of Pikachu, Black Fog are able to consume an enemies soul, they are much stronger than Gastly, Haunter, or Gengar and seem to have the power to control other Ghost-types.
A Giant Haunter, which only referred to itself as Ghost (Haunter's Japanese name), appeared in Fear Factor Phony, Haunter transformed into this form by merging with several other Ghost-types, including two Gastly, two Duskull, and a Shuppet.
In The Old Chateau, a Giant Haunter appeared in the Old Chateau after the butler's ghost disappeared, appearing from a massive cloud of darkness and lightning, it chased Cheryl and her Chansey, and apparently consumed them. However they soon woke up elsewhere, wondering what happened.
Electric Tale of Pikachu
Black Fog makes it's debut in the Electric Tale of Pikachu, it appears as a Legendary Pokémon which was worshiped in ancient times. Black Fog killed many of the humans and Pokémon living in Lavender town until Ash came to capture it, it self destructed to avoid capture.
- Dream Eater - A move learned by Haunter at Level 39.
- Psychic - A move learnable by Haunter through TM29.
- Night Shade - A move learned by Haunter at Level 15.
- Explosion - A move learnable by Haunter through TM64.
- Self-Destruct - A move that cannot be learned by a Haunter.
- Rock Throw - A move that cannot be learned by a Haunter.