Battle Master

This is a Hex — a class feature gained through that class's own talent choices, not a feat you pick through normal feat selection.

The shaman makes an extra attack of opportunity each round. This ability stacks with the attacks of opportunity granted by the Combat Reflexes feat. At 8th level, the shaman gains the Weapon Specialization feat in a weapon of her choice as a bonus feat. At 16th level, the shaman gains the Greater Weapon Focus feat as a bonus feat, for the same weapon chosen for Weapon Specialization. The shaman doesn't need to meet the prerequisites of these feats.