A gigantic gaseous monster is producing an odor that is simply unbearable. Something must be done!
This errand is available after defeating the Candelabracadabra on The Tombstone Trail.
The Fug is located in the Ghostly Gorge northwest of Hamelin. Use familiars capable of inflicting Storm damage, since the creature is weak against it; don't bother with water attacks - it resists those.
Defeat it and you'll complete the bounty hunt, return to the Swift Solutions to claim your reward.