Beast Brawl I collection was an event that ran September 11 through September 18, 2013. You needed to craft and keep in your inventory 2 Epic Boss Armors - Featherblade Battlegear and Trollforge Platemail - to obtain a key for the October Beast Chest. If you crafted and kept the + versions of the armors, you received another 3 keys for the Beast Chests and a limited edition cape. There is also a Beast Brawl II Boss Collection which happened several weeks later.
The first epic boss armor in the Beast Brawl I collection was the Featherblade Battlegear. You obtained it by defeating the epic boss Corvus 15 times to obtain 50 Radiant Feathers to craft the armor. The armor and boss were both Air mono-elemental.
The second epic boss armor was Trollforge Platemail. It was obtained by defeating the epic boss Troll King 15 times to obtain 50 Bone Crown Fragments to craft the armor. The armor and boss were both Earth mono-elemental.