Goblin Skin

In a thick glass jar, topped with a waxed hide lid, lie some mottled and crumpled greyish green examples of the hide of the first generation of goblins. The card that accompanies this specimen goes on to explain that a priest named Ulf of Lundby had been taken captive from Hoabb in its final days under the rule of King Harvald. He was handed over to Eirsom Abbey, while the rest of his captive countrymen were held in a stockade nearby to be ransomed later.
Under the new moons when the Bargain of King Harvald wrought its effect, Ulf was in his cell at the abbey and immediately gained the attention of the monks with his screams. His transfiguration into three goblins had multiple eye witnesses, and the fiendish abominations were bludgeoned unconscious by the terrified monks. A pair of clerics recovering from injuries of their own during the war were at the abbey, and were able to determine that Ulf's soul had been rent into three pieces and bonded with the spirits of demons to create the goblins. After their contemplations they led a ritual circle with the abbot and the monks to reverse the damage done to Ulf's soul and send the fiends back to the abyss. All that remained at the end of the ritual of the goblins who had been bound in sanctified cold iron chains, were these scraps of Goblin Skin and a naked traumatized Ulf.
After some examination the clerics were certain Ulf's soul was intact again, and activities in the abbey began to return to normal. That was when smoke rising from the direction of the castle and stockade was noted. With the aid of two monks who had prior experience in the war, the clerics set out to discover what had happened. They did not survive the inquiry. It was later determined that the other captives had been similarly transfigured, but into Hobgoblins and Bugbears by virtue of their aristocratic lineages, and had killed their captors and ransacked the village. None were recovered in time to reverse the effect of King Harvald's Bargain.