Oblivion Orb should give Grievous Wounds.

Morellonomicon is a 3000 gold item, It's too expensive to buy just for Grievous Wounds. Similar to Bramble Vest Which give Grievous Wounds before completing Thornmail and Executioner's Calling Which give Grievous Wounds before completing Mortal Reminder Oblivion Orb should give Grievous Wounds before completing Morellonomicon

edit: I'm not saying the item is weak, I'm just saying that the whole purpose of buying the item comes too late. A lot of investment without the reward You're looking for until you complete the item. Oblivion Orb should give Grievous Wounds and only some ap