Under Wusao Mountain - Act 3 Story Quest
Under Wusao Mountain is the 4th main quest of Act 3 and begins by speaking with The Yellow Emperor (pictured above). This quest starts immediately upon the completion of Journey to the Jade Palace. First thing you'll need to do for this quest is to return to Chang'an, you can port here if you want but you'll be skipping the Three Sisters Side Quest which I recommend you complete.
Note: This is a very common part of the game to get lost on since when you leave The Jade Palace you'll be taken on a path right back to Chang'an.
From the City of Chang'an you will want to go out the eastern gate of the town. Previously this gate was locked to you but now that we've finished the Journey to the Jade Palace quest it'll be unlocked. If you're having trouble finding this gate, from the Chang'an portal you will need to go a little bit to the southeast.
There will be a soldier by the name of Jing Ke guarding the gate (pictured below). Speak with him and the gate will open then you'll be able to continue to the Forest of the Ancients and to areas beyond.
Once you find the Wusao Mountain Portal in Wusao Barrens you should adopt the approach of skipping every single enemy possible, at least on Legendary. Throughout Wusao Mountain you will encounter Gilded Dead Skeletons which dispell all of the buffs you have on you and white and blue Dragonkin (Ancient Dragonians) which deal an absurd amount of Bleeding and Pierce damage.
The Ancient Dragonkins come in a few forms, they can be casters, archers or melee - the melee are typically the ones that hurt the most. Even the most tanky build I have ever played (as you see in the screenshots I have 11k HP since I am Defense/Nature) still did not comfortably kill these enemies. I had to pop Potions and Rally constantly and run around while my pets did all of the work for me.
Even if you can handle the Dragonkin enemies, if you accidentally run into a pack of Gilded Dead while fighting them and you get all of your buffs stripped off of you - you're dead. This is why I recommend just skipping all of the trash in this mountain, it's far too difficult and annoying for almost all players.
At the bottom of Wusao Mountain you'll find the Telkine we're after freeing the imprisoned Typhon, approach him to start the penultimate boss fight of Act 3. This boss is a commonly farmed boss due to how easy it is and that he is in Act 3 which means that he has access to better loot tables than many of the bosses before him.
This Telkine is also the only enemy in the game with a chance to drop the Adamantine Sickle of Kronos. For the most part this weapon is an Easter Egg of sorts since it has such absurdly high Strength requirements, however there are some builds that can use it. If you'd like to learn more about farming this Telkine check out my Act 3 Ormenos (Telkine) Farming Guide for more information.
Ormenos can be a tough fight if you lack good Vitality and Cold Resistance. He deals some Physical damage but it isn't significant, assuming you can resist the majority of his Vitality and Cold damage you'll be able to easily pop potions to counter any physical you take.
Below is a list of all the abilities you can expect Ormenos to use.
Collapse Ceiling: Rocks will fall from the ceiling and do heavy damage to anyone who is hit.
Energy Blast: One of his typical Energy attacks. Deals Vitality and Cold damage as well as interrupts Skills for 3 seconds.
Short Range Energy Blasts: Much like the other Energy Blast just more commonly used. Deals Cold and Vitality damage.
Summon Fire Imps: Creates 4 Magma Sprites which will assist him in battle.
Telekinesis: Picks up a rock from the ground and throws it at the player dealing a lot of Physical Damage.
After you defeat Ormenos the Under Wusao Mountain quest will be completed. You will also be able to go through the same portal that Typhon did earlier, clicking on this portal will begin the next and final quest of Act 3, Olympus.