Shadow Orb +1

This artifact was imbued with special powers by the Orc Shadow Council. It increases your attack power by 1.

Source
Maiev can find this in The Tomb of Sargeras, chapter 3 of the Frozen Throne sentinels campaign, Terror of the Tides.

This is the initial item that you receive when Maiev first finds it. It begins an optional quest to obtain the remaining nine Shadow Orb Fragments.