The Enderman Relic is an ancient item with the ability to turn Endermen into Brainless Endermen. It is created by crafting 2 different pieces Shattered Enderman Relic together.
It was removed as of version 1.6
To create an Enderman Relic, you need to gather 2 different Shattered Enderman Relics. The first piece can be found in the Enchanted Island biome, picking it up will cause an Endermanpocalypse, of which the final mini-boss (Ender Demon) will drop the second piece when killed. Then it can be combined into a repaired Enderman Relic by placing it into a crafting table in any shape.
By having it in your inventory, all attacking Endermen will be turned into Brainless Endermen as soon as they get close to you (they still have a chance of hitting you). Every time this happens, the item loses one durability.