Miasma

The Miasma is a craftable Hardmode wand. It fires a random spread of five to eight fast gas cloud projectiles that slows down every time they hit an enemy, until it reaches a stop. After being stationary for a short time, the clouds decay into dust and disappear. Clouds can pierce up to nine enemies and also inflict the Irradiated debuff.

Trivia

 * A miasma is a highly unpleasant or unhealthy smell or vapor.