A More Aggressive Method  

Nightmarsh shroomlings have infested the Wanderlust Fair. It's time to try something more aggressive:

1. Vorlin sends you to Madam Victra.
2. Madam Victra gives you a hungry boarfiend (which is a dumb pet that will follow you) and sends you back to Vornlin.
3. Vornlin wants the boarfiend to eat the shroomlings. Go back to the Nightshadow Bog and start killing Nightmarsh shrooms again. The boarfiend will automatically gobble up shroomlings.
4. After a couple of kills the boarfiend explodes.
5. Return to Madame Victra for another boarfriend if yours explodes before the quest updates.
6. Once quest has updated, return to Vorlin for final update and lead-in to next quest in that series.