Nobody ever accused Borderlands 2 of lacking in secrets, but this latest DLC, T.K. Baha's Bloody Harvest, is rife with them. You may think that your fight is over after you've defeated the Pumpkin King, but in fact your journey's just beginning if you want to collect all of the Easter Eggs this DLC has to offer, including a brand-new secret boss battle against an enemy called Clarke the Combustible Crypt Keeper. 

To get this boss battle, you'll first have to get all the other Easter Eggs. When you return from slaying the DLC's first boss, you may notice that one of the mausoleums in front of you has caught on fire, and that there is now a pumpkin underneath of the mausoleum. This represents that you have completed one of the tasks necessary to summon Clarke the Combustible. Lighting the rest of the mausoleums will summon him for an epic, super rare battle. 

Examine the symbols beneath the mausoleums to get a clue as to what you're supposed to do to light that particular mausoleum. The second mausoleum has a cauldron under it, while the third has a giant cow skull on it, and the fourth has a TV. Be on the lookout for all of these items.

To get the cauldron, run up the path to the left and pass by the church. You'll find a massive cauldron in the back of Lavashore Village. Head up to it and drop one gun, one shield, and one grenade into it from your inventory. Note that you won't get these items back. 

Next up is collecting all of the TV collectibles. Here's a guide to finding them all if you've been having trouble with this task. 

Now that you've gotten all three TVs, you need to find the cow skull. This one's not too subtle - check out the steeple of the Church of the Dead and you'll find the skull you're looking for. However, this ties in to collecting six jack-o-lanterns, which are hidden much like the TVs. Again, we've made up a separate guide for this part because this is a bit lengthier of a process. 

After collecting all of these items, head back to the mausoleums. This will unlock the DLC's secret final boss fight against Clarke the Combustible Crypt Keeper.