The key is a random reward for finishing the Wormfeeder Rune task, for which you have to kill 50 enemies without dying. It will always reward you with a chest key, albeit a randomly chosen one every time. Before you can complete this task you have to find Wormsinger Rune. Check out our guide How to use and collect Wormsinger rune. You can also get the key as a drop from enemies on Patrol.
Where to find Ur chest
Start patrol on Dreadnaught. After you spawn, jump off the ledge ahead to the lowest level. Turn around, and go into the hallway. Turn right at the first crossroads, and you’ll see the chest by the wall.
