The Corrupted Pyre Oak is a rare spawn boss creature found in the Burning Wood section of the Graveyard that only appears in the nighttime hours (Gloaming to Dawnsong).
Walkthrough & Notes
Keep a look out for the Corrupted Pyre Oak. It spawns in the Burning Wood area of the Graveyard, the valley to the southwest. It is found right near the edge of the Graveyard around 66.5S, 44.8W. Remember that it only spawns during the night and disappears at Dawnsong.
If you are lucky enough to be around when he spawns immediately summon reinforcements. It is not easy to fight alone and has a great deal of health.
The golem spawns with a number of Corrupted Pyre Sparks that cast level 8 Fire Vulns so it is best to avoid them completely. It also has many of the normal spawns of Pyre Skeletons near it.
The absolute best way to kill it is for archers kill it from afar with using Spectral Bows with Lightning Arrows (Raider Lightning Arrows preferably). Archers should be able to find a spot outside the agro range of the creatures (Sparks and Skeletons) where they can fire on the golem. The Sparks will not defend the golem. Mages should just support the archers and debuff the golem. Melees should also just heal because it is normally too dangerous to jump down into the fray.
The Pyre Oak's most dangerous attacks are fire attacks including Flame Wave and Fire Bomb. When fire vulned these spells do tremendous damage and can even one shot you.
His corrupted forest form destroyed, the spirit of Lord Grymar appears.
Lord Grymar says, "I can linger in this wood for only a short time. Come speak gentlefolk."
Ranger Lord Grymar Mhoire tells you, "The corruption of my spirit binds me to these trees. I can feel the burning of the wood as if it was my own flesh."
Ranger Lord Grymar Mhoire tells you, "You have my thanks for becoming watchers of this wood, however burnt. Take my key and seek my hidden vault. The treasures there are yours."
Ranger Lord Grymar Mhoire gives you Lord Grymar Mhoire's Key
Ranger Lord Grymar Mhoire tells you, "I thank you for your skill and bravery."
Ranger Lord Grymar Mhoire bestows to you the title "Warden of the Burning Wood."
Giving Lord Grymar's Ancient Emblem of Mhoire to Arcanum Mana-smith
You allow Arcanum Mana-smith to examine your Lord Grymar's Ancient Emblem of Mhoire.
You hand over 1 of your Lord Grymar's Ancient Emblem of Mhoires.
Arcanum Mana-smith tells you, "Here's an interesting bit of information for you. Mhoire had his family's emblems infused with a small bit of mana - enough that I can use it in the forges successfully. I'll give you a key - one of the special keys, not my normal keys - in thanks."