Vengeance of the Illidari

Vengeance of the Illidari is a trinket. It gives a bonus to critical strike.

Source
This item is a reward from Overlord (quest) and Cruel's Intentions.

Effective Spell Power
Assuming this trinket were activated every cooldown, it would grant an effective: 120 * 15 / 90 = 120 * 1 / 6 = 120 / 6 = 20 Spell Power