Read from the World of Warcraft client build files.
How Cobalt Guardian's Helm Compares
Who It Suits
Mail is the armor type Evoker, Hunter and Shaman wear. With Agility or Intellect, Cobalt Guardian's Helm suits Beast Mastery, Marksmanship and Survival Hunter; Elemental, Enhancement and Restoration Shaman; Devastation, Preservation and Augmentation Evoker.
Transmog Sets
Cobalt Guardian's Helm is part of the transmog set Dracthyr Battlegear. The other 16 pieces:
Blizzard numbers items as they are created, so the named items next to ID 191831 (191826 to 191836) were usually added in the same batch as Cobalt Guardian's Helm: the same quest line, zone, vendor or reward set.