There are a couple of enemies outside on the World Map. Other than that, there’s nothing to worry about, so go on and enter the deadly marshes. Once you’re inside, Esther will clear them out for you with the Clarion. After a scene, you will be able to explore the Quagmire of Corruption! (Giggity!)
Before moving, you’ll want to cast ‘Levitate’, and keep it on the entire time. The whole area is covered with random poison traps, so use the spell and keep an eye on the icon in the upper left corner; if you see it start to blink, cast it again, and be careful NOT to touch the ground.
Use the Waystone if you need to, then proceed northwest to a fork. Open the chest to your left first to find an [ESPRESSO] , then return to the fork and make your way to the far northwestern dead-end for a blue chest containing a set of [DEAD MAN’S DUDS] . Head back to the Waystone to heal, then proceed northeast, going all the way up when you can to find another chest at a dead-end. Open it for an [ALL-BE-GONE] .
Head down from that chest now, and you’ll soon come to an open area / awkward fork in the path. Take a few steps north, then turn east to find a red chest near the water with a [FRUIT FLAN] inside. Turn left, then you’ll be at another split as you go up. Continue up, then go right and down to find a blue chest at a dead-end; unlock it for a [FIEND’S FANG] .
Go back to the fork and continue west, then a tiny bit north to be at another somewhat open fork. Head up and to the right first, grabbing the [TONIC] at the dead-end here, then return and go slightly left, then down. You’ll come to another dead-end down here to the left, along with a nice purple chest. Unlock it for a suit of [NIGHT ARMOR] . Return to the fork, then go northwest, moving up as you go, but stopping before you turn right.
There’s a green chest to your west, so go up against the upper left edge here to find Swaine’s vantage point, allowing you to snipe a bottle of [SPRITE DEW] . That’s it for treasure, so head right and follow the path to another Waystone. Use it, then proceed northwest to take on the evil Vileheart.
Boss Fight: Vileheart
After the battle, watch the quick scene before you regain control in a different area. Just go forward to progress the story, the watch the story unfold in a major way.
You’ll eventually regain control of Esther in Perdida. Head south to the exit for another long set of scenes between Esther and Swaine, then with Oliver. It will all lead to another battle with Vileheart, but this time, with the ultimate [MORNSTAR] spell in his possession!
Boss Fight: Vileheart
After the battle, make any preparations needed before heading to Nevermore. When you’re ready, use ‘Travel’ to go back to the Miasma Marshes, then proceed to the magic circle in front of you. It’ll take you back to where you fought Vileheart, so from there, just travel northwest and follow the path to enter Nevermore!