Arcanist's Stone

Source
This item drops from the Epoch Hunter in the Old Hillsbrad Foothills wing of the Caverns of Time on Heroic mode.

Effective Spell Power
Assuming this trinket were activated every cooldown, it would grant: 167 * 20 / 120 = 167 * 1 / 6 = 167 / 6 = 27.83 Spell Power