Read from the World of Warcraft client build files (JournalEncounterItem, JournalEncounterCreature, Achievement) and the Blizzard Game Data quest API.
How Mardum Chain Helm Compares
Who It Suits
Mail is the armor type Evoker, Hunter and Shaman wear. With Agility or Intellect, Mardum Chain Helm suits Beast Mastery, Marksmanship and Survival Hunter; Elemental, Enhancement and Restoration Shaman; Devastation, Preservation and Augmentation Evoker.
Transmog Sets
Mardum Chain Helm is part of the transmog set Darkwatcher Bindings (Hunter, Shaman and Evoker only). The other 16 pieces:
Blizzard numbers items as they are created, so the named items next to ID 134387 (134380 to 134392) were usually added in the same batch as Mardum Chain Helm: the same quest line, zone, vendor or reward set.