Tome of Arcane Phenomena

Source
This item can be found inside the Cache of Eregos after defeating Ley-Guardian Eregos in The Oculus on normal mode.

Effective Haste Rating
Assuming this trinket were activated every cooldown, it would grant an effective: 256 * 20 / 120 = 256 * 1 / 6 = 256 / 6 = 42.66 Haste Rating At level 80, this equates to: 42.66 / 32.79 = 1.30% Haste