While in Aseir, preferably in Co-op mode, go to the mission selection screen, and choose mission 3-4. Go through this mission until you reach a bridge with two enemies you must kill. After this, you will go through one more door where you will kill a troll, a spider, and then another troll. At the location of the last troll, there will be a door in front of you and a pathway to your left which leads to a well. From here, walk through the door, and have another player stand by the pathway. Walk through and kill all the enemies, including the spider. Once they are all dead, have the other player walk across the path towards the hallucination well. Doing this will respawn you back to the path where your friend is located. You may go through the door once more to kill all the enemies. You can do this as many times as desired. To do this while not in Co-op mode, follow all the steps previously described, except you must stand in front of the door so it stays open. You must then shoot all the enemies including the spider. Once they are all dead, go to the exact pathway previously described. You will return to the door, and all enemies will respawn. Doing this long enough will result in an Epic item. Note: After doing this many times, if the spider does not drop any Epic or Red items, return to Asier to reset the random drop generator to give you a better chance of finding those items.
I don't take credit for this it was founded by my friend.