Umbra is a Spirt/Earth Element Epic boss that lasts from June 9 to June 16 of 2015. Umbra drops the Umbra Gems, which can be used to craft the Voidbane Wargear after obtaining 50 gems. Umbras Nemesis Armor can be gained through the Dark Prince's Chest during this event.
The Graph below contains the rewards that can be gained through the current boss.
|1||7 Umbra Gems, 5,000 Gold, and 5 Epic Energy|
|3||4 Mystic Armor, and 3 Silver Keys|
|6||12 Umbra Gems, 5 Epic Energy, and 4 Mystic Armor|
|10||15,000 Gold, and 5 Chimera Corps Uniform|
|15||15 Umbra Gems, 10 Mystic Armor, and ability to Craft the Voidbane Wargear Armor|
|21||1 3 Start Ring, 15 Chimera Corps Uniform, 3 Fusion Stars, and 1 Gem|
|28||1 3 Star Amulet, 10 Epic Energy, 5 Enchanted Keys, and 15 Chimera Corps Uniform Armor|
|35||5 Super Rare Armor (name unknown at time), 2 Gems, and 3 Fusion Stars|
|43||5 Super Rare Armor (name unknown), 5 Enchanted Keys, and Ability to craft the Voidbane Wargear|
|51||10 Super Rare Armor (name unknown at time) and 5 Fusion Stars|
|60||5 Dark Prince Keys, 10 Enchanted Keys, 5 Gems, and 3 Ultra Rare Armor (name unknown)|