A series of hidden jack-o-lanterns in the latest Borderlands 2 DLC links back to the Church of the Dead, and unlocks a super secret boss battle against Clarke the Combustible Crypt Keeper. To find out how to get this boss, check out our guide. You'll have to nab all of these pumpkins first, though.

To nab the first jack-o-lantern, head past the gate that you unlocked using Sulley's Key. It'll be sitting on a bluff to the upper right of the entryway. Shoot this pumpkin, and the first part of Clarke the Combustible's soul will be released into the air. You're going to want to shoot all the rest of the pumpkins in the same way.

The second jack-o-lantern is found in the houses of the Lavabluffs. As you head down the stairs towards the bridge, you'll come upon this second pumpkin on the ground. Follow the spirit that leads out of this one to head towards the third jack-o-lantern, which you'll find in the cemetary on top of a rock ledge. 

Loop back around to the start of the level, where you'll find the fourth pumpkin by the bridge. Cross the bridge after shooting the fourth jack-o-lantern, and enter the cemetary. Hang a left and head over to the mausoleum. Shoot the pumpkin on top of it to activate it. The sixth and final jack-o-lantern can be found up in a tree to the left of the gate you unlocked with Sulley's Key. You'll have to zoom in and look up, because this jack-o-lantern is looking down over the entire level from its lofty perch.

Now that you've activated all of the jack-o-lanterns, you'll notice that the torches around the Church of the Dead have activated, allowing you to fight against the Clarke the Combustible Crypt Keeper boss.