The Hero's Challenge

Overview
Summary Obtained from
 * 1) Enter the Frozen Forest from the Iron Mines of Moladune.
 * 2) Follow Sanyi through the mountains.
 * 3) Defeat Sanyi the Soul Eater.
 * 4) Return to Vanyi for your reward.
 * Vanyi in Droknar's Forge

Requirements
 * Complete a single profession path quest:
 * The Elementalist's Path
 * The Mesmer's Path
 * The Monk's Path
 * The Necromancer's Path
 * The Ranger's Path
 * The Warrior's Path

Reward
 * 5000 XP
 * 15 Attribute Points

Dialogue
 * "Your aura is radiant. Aided by the spirits of the desert, you can learn any profession, master any skill, but there yet remain untapped reserves of power within you.  Take my advice, go to the Frozen Forest from the Iron Mines of Moladune, and seek out my sister Sanyi.  She will help you unleash this hidden power."

Walkthrough
. You can also take the walk from Droknar's Forge or Ice Caves of Sorrow.

When approaching Sanyi (you don't have to speak to her, just walking near her is enough) she will request you to follow her through the mountains and start walking. You will encounter some monsters unusual for this area: Two level 22 Mragga Spawns, which are easy enough to kill or avoid. From the exit of Copperhammer Mines she will head to the left down into a valley which is swarming with Stone Summit. They won't attack her, but unfortunately she will stop there until you walk close to her again, running the risk of aggroing a horde of enemies. You have two options: clearing out the whole area of every single dwarf (requiring a quite strong party and careful maneuvering), or simply waiting a bit until the mobs have strayed far enough away from your aggro bubble to safely approach her.

Sanyi will resume her slow progress further to the left up into a narrow valley where she'll wait for you to speak to her again. After walking close to her again, Sanyi will start talking once more and finally transform into the demon Mragga (level 28 Necromancer). She will also summon three more Mragga Spawns to her aid. Compared to the hordes of enemies you have faced on your way here, this fight is ridiculously easy. Take her down first, then her allies, and return to Vanyi (who will have a perfectly plausible explanation for this) for your reward. Necromancers may want to use the Signet of Capture to acquire Grenth's Balance from Mragga.