This is the last mission in the Hammerlock's Hunt campaign. It is pretty straight forward, the only hard part being the boss, Jackenstein. In order to defeat him, you have to keep shooting the electric barrels on his back until they explode.
It will seem like you are doing very little damage to him, but once the barrels explode the majority of his health will be gone.
After the barrels, shoot his chest until that also explodes. He often stood on his hind legs, giving the perfect chance to lay a bunch of shots into his chest.
If there's any way I can improve this, please leave a comment. Thanks and good luck!