The path from Perdida to the Miasma Marshes has opened up again... Go and find out what's going on.
This bounty is available to complete after beginning Errand 131.
This is a rehash of the Vileheart fight, so travel to Perdida, then go into the town and exit to the north to be back at the Miasma Marshes! Levitate your way to the open area at the end to find another black orb, and thus, the next boss: Bileheart!
As with Vileheart, your main concern is the Viledriver. EVERY time you see it coming, use Defend and All-Out Defense to minimize the damage. His other attacks are nothing compared to it, so in the meantime, buff your party and deal out physical attack as usual, since he's somewhat resistant to magic. You were probably more likely to have a problem with Cerborealis than you will with Bileheart. As always, stay healed.
Defeat it and you'll complete the bounty hunt, return to the Swift Solutions to claim your reward.