WoW Heirlooms — Browse All Heirlooms
Track your World of Warcraft heirloom collection. Browse all 134 heirlooms with vendor locations, costs, and upgrade levels. Filter by armor slot and weapon type.
Browse all WoW heirlooms with upgrade levels and acquisition sources. Find heirlooms from vendors, achievements, and special events. Track which heirlooms you own and their upgrade status via Battle.net.
Discerning Eye of the Beast
Source: Vendor: Estelle Gendry.
The 
Discerning Eye of the Beast is a spellcaster heirloom trinket that restores 2% of your mana per killing blow on a green or higher enemy, and is purchased from a vendor in Silvermoon City.
Locate Enchanter Erodin
Find Enchanter Erodin at 41.8, 66.4 in Silvermoon City to purchase the Discerning Eye of the Beast.
Purchase The Trinket
Buy the Discerning Eye of the Beast for either 50 Emblem of Heroism or 
75 Champion's Seal. If you plan to equip two copies, the total cost is 100 Emblem of Heroism or 150 Champion's Seal.
Tips
The trinket has no internal cooldown, so killing multiple enemies simultaneously returns 2% mana for each kill — wiping out 10 mobs at once returns 20% of your total mana pool.
You must land the killing blow yourself for the mana return to trigger; this also works on enemy totems and wards.
Running two Discerning Eye of the Beast trinkets stacks the effect, returning 4% mana per killing blow instead of 2%.