Introduction

To enter the Blighted Grove you must have a Bone Machete in your backpack. This item can be crafted by Blacksmiths who have learned the recipe from Jamal the Fisherman, who can be found outside the dungeon.

To gain access to the Peerless boss, Lady Melisande, you must complete a quest from the Frightened Dryad found in the dungeon. This quest involves kiling 12 Insane Dryads and the named Harpy Saliva. The reward from the quest can be dropped into the basket next to the dryad, which will result in a number of teleport items that will take you to the peerless area.

*Note: Peerless Bosses will only spawn in Felucca

Entrance

The entrance to the Blighted Grove can be found just southeast of the entrance to Dungeon Shame, right next to a small corrupted lake.

Spawn Guide

Abscess
Bog Thing
Bogling
Changeling
Coil
Corpser
Giant Serpent
Giant Toad
Harpy
Hydra
Insane Dryad
Reaper
Saliva
Silver Serpent
Tangle
Thrasher
Whipping Vine

Summoning Lady Melisande

To get to the peerless boss Lady Melisande you must complete Bound to the Land quest. She is just down and to the right of the entrance to the grove. She will ask you to kill 12 Insane Dryads and one Saliva.
Saliva is a blue, named harpy that is roughly the strength of a paragon harpy. To locate her, run up the tree root to the left of a entrance and into the wall covered with vines at the top of the tree root. You will emerge inside a small cave with her in it, but beware, she has other harpies and changelings guarding her. I highly suggest casting invisibility before you run into the cave. Once inside pets or summons can clean out the cave pretty well. The fetid air inside Saliva's cave will slowely drain your health and interfere with spell casting.
The entrance is one-way. To exit, you must run to the other end of the cavern.
The insane dryads that must be killed for the quest are not hard. However, they will becalm you, so be prepared. You have to do a good chunk of damage to them to get credit for the quest, as individuals. To find the dryads run past the gnarled looking trees, they will pop out and chase you. They are on what appears to be a 5 minute spawn timer. Watch out for the named monsters while dryad hunting, they can make life hard and death easy.
These keys are considered to be the easiest to get. As a result, at least on the Lake Superior shard, it is fairly easy to find a group of people at the entrance, waiting for a spontaneous group to get in.
The "first key" is the Dryad's Blessing. This is exchanged for the "main key," the Dryad's Curse, at the basket that's right near The Frightened Dryad.