- Base of Atiesh
- Quest Item
- Unique
The Base of Atiesh, Greatstaff of the Guardian is the only piece that is not in Naxxramas. It is available to players who have collected the 40 [Splinters of Atiesh] from Naxxramas and who have formed the [Frame of Atiesh], and received the quest from Anachronos to obtain both the base and the Staff Head of Atiesh. This item is needed to complete the quest rewarding in [Atiesh, Greatstaff of the Guardian]. Once the frame and base have been attained, only the head - in the hands of Kel'Thuzad - remains.
Source
The Base of Atiesh drops off C'Thun in the Temple of Ahn'Qiraj for players who have the quest 
[60] Atiesh, the Befouled Greatstaff.