After talking to High Priestess Isidora in the last quest Aten Rising, in the next main quest The Heretics you will head towards the second boss of this DLC. The Heretic is a Level 48 Main Quest with an reward of 10000XP.
The Heretic Walkthrough
The Heretic will unlock once you finish Aten Rising. Mark the quest through game menu and your mission begins.
Where To Find and Get Tychon’s Ledger
In the first objective, you will have to find Tychon’s ledger. Head towards the Temple of Hatshepsut. Go on the top floor, and kill Tyhcon to get his ledger.
Where To Find the statue of Amun-Ra
After getting the ledger you will have to hunt for the statue. If you attack Tychon in the daytime a lot of soldiers around will attack you. The statue is in the treasure area of the temple. To get there, the place where you get the ledger is the top floor, just outside the room, there are stairs that will take you down. Follow it and turn right, keep going straight and you will reach in an open area.
Take the entrance marked in the image above, it will lead you to a closed door. The statue is behind the door. Take the first exit from your left and keep walking till the end, turn right and the first left you will get a small window. Enter through the window and look to your right for a huge stone statue. Interact with the statue for a cutscene.
How to Reach the tomb of Akhenaten
This is location is a bit far from where you are right now, try using a fast travel point. Enter the tomb and glide through the afterlife point. You will have to find your way through the Am-Tuat. Fight with a few enemies and keep moving forward. Jump in the water and swim towards the other side.
How to Examine the Guardian Statue
Once you are out of the water on your left side you will find the Guardian Statue. Next, you will get an objective to destroy all the symbols of the Aten. The first one will be in the hands of the statue, the round object, just destroy it. There are around four more scattered around the new area. Watch out for the crocodiles near the water. They are Level 49 enemies that can cause you a good damage. Some symbols will guards and scorpions around.
How to Reach the Akhenaten Throne
Once you are done destroying them all head to the throne. The boss Akhenaten will appear and he is a Level 50 enemy. Watch for the red glow around and the yellow one. The red once means a powerful attack, so dodge it and yellow one means the boss is trying to regain health. You will have to interrupt, you can do this by throwing fire bombs or by using fire arrows. One single charged attack of this boss can eat more than 80% of your health. So try to be fast and keep moving around. Don’t stay in a single direction. If you are somewhere at Level 47 you can defeat the boss with some struggle. After killing him you will get The Living One Sickle Sword and 10000 XP. The sword is a Level 48 weapon with 528 damage per second and 108 Quality.