Black Fog was once worshipped by the people of Lavender Town in the past, causing it to grow arrogant and prideful. It had attacked several Trainers and their Pokémon and was the reason why Sabrina only had one Pokémon with her.
Black Fog had made its appearance again by preying on Trainers, but they were saved by Sabrina, who had taken the brunt of Black Fog's attacks. Later, it battled against Ash and Brock's Pokémon, overwhelming them with its Psychic, causing Sabrina's Abra to help them counter its Psychic, which enabled Ash's Pikachu to hit it with a Thunder. When Ash attempted to catch it using a Poké Ball, it chose to Self-Destruct rather than get caught out of pride.