Very rarely, a sudden mutation can result in two small Koffing twins becoming conjoined as a Weezing. Though very rare, triplets have been found.
Weezing loves the gases given off by rotted kitchen garbage. This Pokémon will find a dirty, unkempt house and make it its home. At night, when the people in the house are asleep, it will go through the trash. It lives and grows by absorbing dust, germs and poison gases that are contained in toxic waste and garbage.
Weezing alternately shrinks and inflates its twin bodies to mix together toxic gases inside. The more the gases are mixed, the more powerful the toxins become. The Pokémon also becomes more putrid. If one of the twin Koffing inflates, the other one deflates. It constantly mixes its poisonous gases.