Read from the World of Warcraft client build files (JournalEncounterItem, JournalEncounterCreature, Achievement) and the Blizzard Game Data quest API.
How Shadow Archer's Helm Compares
Who It Suits
Mail is the armor type Evoker, Hunter and Shaman wear. With Agility or Intellect, Shadow Archer's Helm suits Beast Mastery, Marksmanship and Survival Hunter; Elemental, Enhancement and Restoration Shaman; Devastation, Preservation and Augmentation Evoker.
Transmog Sets
Shadow Archer's Helm is part of the transmog set Armor of the Skyfather's Chosen (Hunter, Shaman and Evoker only). The other 16 pieces:
Blizzard numbers items as they are created, so the named items next to ID 139244 (139239 to 139249) were usually added in the same batch as Shadow Archer's Helm: the same quest line, zone, vendor or reward set.