Nirvana: Vanished Ancestor

In order to beat Vanished Ancestor, you will need to Seal the random Elemental Add that will spawn using the appropriate Seal against it. For example in the chest of WATER you will get the Seal to beat the FIRE mob (from chest of water you pick up the item "Fire Proof"). 

Once you get the Seal, it will be in your inventory. To use it on the Add, you have to target the Add and right click the item you picked up. Once that's done, your job is over! Until the next Add appears....