First you need to get the three scrolls after killing Arishock in Act 3. Each scroll marks a hidden lair on your map. So you have to go through each side quest and kill the Hidden Lair Monsters.

Here are the locations of the 3 Awiergan Scrolls: (X marks the location of the scroll)

First Aspect – Location: The Wounded Coast

Second Aspect – Location: Sundermount - After getting the scroll, travel through the sundermount passage to find the Hidden Lair.

Third Aspect – Location: Sundermount

Go to Darktown and in the Hidden Lair marked on map you will find Hybris.
Prepare for a tough battle with Hybris. Make sure you have stock up potions. It recommended to have a tank, a healer and 2 damage dealers to easily kill him.  Make sure the tank gets the attention of Hybris so he takes all the damages. Don’t forget you can pause the game so you can easily plan your strategy. You can always change the difficulty level when you die.

You can watch the video here