Common causes of pain in the back of the head are different types of headaches, like tension, migraine, or exertion headaches. In some cases, pain in the back of the head can signal a more severe ...
The Ulcerated Tree Spirit (Stormveil Castle) will appear as soon as you land. Defeat it, then progress south to find Godwyn's head, and the Prince of Death's Pustule next to it.
As suggested by its name, GPP typically presents as pus-filled blisters (i.e. pustules) on reddened skin, which can affect large areas of the body.