Mysterious Half Arch

 is a rare base item.

Obtained from

 * Justice League Dark: Loot Cache
 * Justice League Dark: Large Loot Cache
 * Justice League Dark: Large Treasure Box
 * Justice League Dark: Small Treasure Box
 * Justice League Dark: Treasure Box
 * Justice League Dark Base Item Box
 * Justice League Dark Large Base Item Box

Feats

 * Nothing Really Mattress: Collect 1 Base Item from Justice League Dark (10 points)
 * Bookshelf Esteem: Collect 10 Base Items from Justice League Dark (25 points)
 * Grand Theft Ottoman: Collect 25 Base Items from Justice League Dark (50 points)