I believe (I HOPE) Howling Feast is bugged, or the description is just incorrect. At max level it increases Hero Damage by 30 after you get 10 Feast stacks. This is a very insignificant damage increase, and there are requirements for getting the buff. Please verify that 30 damage is correct. A single Ascension point into Hero Damage is 20, needing to land 10 attacks in 3 seconds in order to gain 30 bonus damage is a horrible waste of a Shard Slot if this is correct.
I will also add that this Shard does not work on Abyss Lord, but there is no tooltip indicating it shouldn't.