The Emperor's Clay Soldiers is a side quest in the Orient (Act III). There's a bug related to this quest, which may prevent you from getting a part of your reward (see below).
The quest is given by Ma Feibai, a guard captain standing at the western entrance of the City of Chang'an. He will tell you of the Great Emperor's clay soldies, who have become alive and are now about to overrun the city. You are sent to the Mausoleum to look for the source of this chaos.
The 'Mausoleum' is the Chang'an Palace located behind one of the large wooden gates leading to the north-west. In the Palace you will encounter Bandari - Terra Cotta Sorcerer, a boss enemy you need to kill in order to progress with the quest. He is of moderate difficulty, but uses spells to slow you down and to create a volcanic eruption, similar to the one from the Earth Mastery. He has also the ability to teleport himself around in the palace and is guarded by a couple of Terra Cotta Warriors.
When you have defeated Bandari, go to the north-western part of the Mausoleum and talk to the Spirit of the Great Emperor to receive the first part of your reward, 2 Attribute Points (see bug note below). Head back to Chang'an and talk to Ma Feibai again to get the rest of your reward and to complete the quest.
Reward: 2 Attribute Points (from the Spirit of the Great Emperor), 30000 Experience, random Amulet (both from Ma Feibai).
Bug Note Edit
When you leave the mausoleum after having Bandari defeated but before having talked to the Spirit of the Great Emperor, the spirit will disappear and you won't be able to get the 2 Attribute Points reward from him anymore. The Fanpatch provides a solution for this situation: If you missed this reward, go visit Laches, a guy standing next to the Portal in the Village of Helos (the first city in the game) - he will recover the reward.