Staff of Cairn is an artifact in Tyranny.
This staff resembles the arcane tools wielded by Earthshakers. What separates it from its peers is a fragment of the Archon of Stone fused with Azurelith gathered in the Stone Sea. As an expression of Cairn's magic incorporating his body as a component, it is safe to regard the Staff of Cairn as possessing the raw potential of an Earthshaker apprentice in a dormant state.
Though Cairn is remembered for his unpredictability and uprising against Kyros, the powers of this staff have achieved a dormant, controlled state. The gem at the head occasionally flickers with violent awareness, but goes still with time.
- Stone Sea: Harvest a piece of Cairn during Securing The Sea and change it into a staff at the Forge.
For staffs created in game (as opposed to imported through New Game+), the stat bonus increases with reputation, up to +7 for Wits and +6 for Quickness (haven't tried the others).
Also seems to be bugged depending on the playthrough, as the staff or the Reforged piece of Cairn seem to not always be both displayed on the selection screen for the Forge. Entering Act III or researching a new Artifact seem to solve this problem (sometimes). Reloading from before you got the Fragment and cleaming up the list of unique Items also can solve the problem.