Disclaimer: In a nod to Oscar Wilde, I own nothing in this story but my genius. :)
Sam entered the mine alone. Dean was at the motel recuperating from the last job, and this was a simple case of goblins from the old country. Sam stretched his massive shoulders thinking goblins shouldn't be too much trouble. The men working the mine complained of mysterious blue lights and a couple of them had been hurt, but no one was really sure how. Reading the lore revealed the blue lights were associated with a particular type of goblin: kobolds that could only be killed by a knife made of cobalt.
Being in coal country Sam was able to coat a big hunting knife with a powder of the mineral before heading out on the hunt. After a couple of hours in the caverns following directions from the miners, blue light appeared ahead of him. Sam went deeper into the cave pulling the long blade from its sheath. He listened to a deep voice singing as he approached the light source; and peering into a blue glowing cavern, he saw a small, sturdy figure wearing a silvery helmet. With no real cover available, Sam decided the direct approach would be best so he stepped into the large open cavern and moved forward.
The goblin looked up and saw the hunter approaching. The creature went toward Sam, growing and changing, transforming into a huge, brown bear. Sam was surprised but continued forward. Goblins weren't supposed to be able to do that. Sam stopped and held his ground waiting as the towering animal lumbered closer. The bear wrapped its massive arms around Sam as he brought the knife up slicing the creature from belly to neck. The bear grunted once with an expression that could only be described as surprised. After it collapsed the animal shrank; drawing into itself; returning to its goblin form. Sam bent over it and with the blue glowing knife removed the creature's head ensuring it was dead. He tossed the head with the helmet still on it into a corner satisfied the job was complete.
The treasure the goblin hoarded glowed in the cavern light, intensifying and reflecting the blue. Sam kicked a pile of gold out of the way as he turned, leaving it for the miners. Before he could move much further, a second kobold entered the cavern. It looked at the dead goblin, stunned that a mere human had dispatched its companion. Its eyes obviously searching for something focused on the decapitated head; it rushed to the repulsive remains; snatched up the helmet; and placed it on its own head. The kobold started moving toward Sam and began changing into a bear. "Déjà vu, all over again," thought Sam. Instinctively, Sam grabbed a stick at hand and swung at the creature. The bear dropped to all fours causing the stick to go high and strike the wall.
When it hit, a brilliant flash of light accompanied by a thunderclap filled the cavern. Sam realized that instead of a stick he now held a short handled sledge hammer. It fit his hand perfectly. Instinctively he swung the hammer, striking the bear at the base of its skull. It dropped like a rock. "Apparently, there was more than one way to kill a kobold," Sam thought. After it changed back to its real form, Sam pulled his blue bladed knife and removed his second head of the day. This time he kept the helmet and holding onto the hammer climbed from the mine.
Dean was lounging on the motel bed when Sam returned, "Hell, Sam, what happened to you?"
Sam furrowed his forehead, "What are you talking about?"
Dean laughed, "You've gone all blond. You trying for a different look? And what's the sledge hammer for?"
Sam went to the wall mirror staring and playing with his long, once brown long hair now totally blond. He told Dean about the cave and what happened in it. Dean didn't read comic books for nothing, "Damn, Sammy. You're Thor and that's the Tarnhelm. You're a Norse god and that helmet let's you be invisible or change form."
"I thought I was supposed to change to become Thor," Sam said.
"Well you went blond. You're lucky you didn't shrink, Sasquatch."
The next morning they were packing the car, carrying the hammer and the helmet Sam asked Dean, "What should I do with this junk?"
Dean answered, "Throw it in the back with everything else. We'll see if we can find something to do with them."
As they drove off, a concerned Sam asked, "Do you think I can find a beauty parlor and get my real hair color back?"