Damn plot sheep wouldn't let this go. Why 'plot sheep'? Well why should plot bunnies have all the fun plus they don't fly around, unlike plot bats.
Onslaught
"Dean did you find anyth...," Sam's voice trailed off at the dazed look on his older brother's face as he stood in the doorway of their hotel room. "Dean?" He walked over and grabbed his brother's arm.
Water dripped off Dean's soaking wet clothes. "Sam, I.."
The younger Winchester pulled Dean fully into the room and shoved the door shut. "Dean are you alright?" Worried, he dipped his head down to look his brother in the eye. Dean was as white as a sheet and about as coherent, seeing his stalwart brother so affected by a milk run recon unnerved Sam. He pulled then pushed the older man closer to and down onto the nearest bed. Kneeling on one knee he looked up into green eyes that wouldn't meet his own. "Talk to me man. What happened?"
He closed his eyes, "Sam, there was…I saw...it's…" Dean shook his head and jerked off his wet jacket.
"You saw what, Dean?"
Desperately grabbing his brother's arms Dean shuddered with barely contained emotion. Fear and concern had Sam gripping Dean's arms back. An evil grin broke out across his brother's face and before Sam could react he found himself slammed against the wall between the beds. His head bounced as he was slammed against the wall twice more. The bedside lamp broke into large shards under the onslaught and the edge of the bedside table bit painfully into the back of Sam's calves. "Dean! What the hell?"
Dean then threw the younger man over the bed to his right, Sam's body crashed onto the dining table which tipped over spilling Sam and everything else onto the floor. He tried to get up but his legs tangled with the computer's power cord and he was left to kick his way backwards away from his advancing brother. Sam wiped blood from under his nose and shouted, "CHRISTO!"
Dean laughed, "not a demon Sammy." He reached down to yank the younger man up at the same time as Sam kicked out with both legs, sending the older Winchester into a backwards somersault.
Sam scrambled up using the wall for leverage, "you're not my brother." Not wanting to get trapped in a corner, he edged around the overturned table and out into the larger main area.
"SON OF A BITCH!" Dean yelled getting back up. "I was just going to play with you bit Sammy, but now," he bent down and grabbed a broken chair leg, "I'm gonna fuck you up bad." He swung the chair leg like a bat the broken end barely missing the younger Winchester's face. As Dean was about to reverse his swing, Sam kicked him in the stomach then stepped in and slammed his fist into his face. He was able to strike one more time before getting hit in his own stomach and struck across the back of his left shoulder with the chair leg.
Sucking in a hiss of pain, he opened his eyes in time to grab hold of the chair leg and push it away just as the broken end was about to skewer him in the neck; holding tight he twisted the piece of wood until Dean let go. Sam grabbed the man's forearm intent on twisting it up behind his back when the skin slid off in a bloody sheet in his hand. Sam jumped back shaking his hand vigorously, the squishy mess dropping to the floor. "Shapeshifter," Sam muttered under his breath looking back at his 'brother'. "What've you done with Dean?" he demanded.
"I am Dean," the shifter laughed, "new and improved." He launched another assault against the younger man. Using a football move that a younger Dean had loved to use against his smaller brother, the shifter threw them back into the long dresser set against the far wall. Sam's head smacked against the mirror, cracking it, bouncing off the mirror they fell onto the unforgiving hard edge of the dresser than landed in a heap on the ground. Being on the bottom, Sam took the brunt of the collision and fall, so as the shifter rolled away with only slight aches and pains; Sam laid in a groggy, bleeding heap. Arms and legs uncoordinatedly flopped about as Sam's scrambled mind tried to decide between fighting, fleeing or passing out.
The shifter grinned maliciously as he pulled Sam away from the dresser, leaving a smear of blood on the carpet from the gash on the back of Sam's head. Barely able to open his eyes, Sam groaned when something grabbed his hair and yanked back his head. Sam saw Dean looking down at him with an expression of disgust. "I can't believe I've held out this long Sammy," the shifter said as he ran the point of a razor sharp knife, snagged from the open weapons duffle, along the younger man's neck, drawing blood. "But I've had a revelation Sammy, everything bad that's happened in my life, to our parents, can be traced back to you. Well no more little brother. From now on it's just me, my baby and the open road," the shifter shrugged, cocking his head, "and possibly your giant, decomposing head in a box…in the backseat." The shifter smiled and tapped the knife blade on the tip of Sam's nose, "or the trunk. I'm still debating…backseat or trunk, backseat or trunk…hmm. Do you have a preference?"
Sam tried to grab the knife but the pain in his head and the double vision made it difficult to focus. "No…don't…" Pain burst through his abdomen, Sam's scream caught in his throat, his back arched and his feet kicked as he tried to escape the fire in his gut. His uncoordinated slapping of the shifter earned him a hard backhand to the face. Letting out a grunt, his arms flopped back to the ground and he could barely see the bloody knife blade being held up to his face. With the loud roaring in his ears he didn't hear the muffled screaming of his name nor the sound of the motel room's door being violently kicked open. He rolled onto his side curling into a ball, his arms wrapped tightly around his middle as a fight ensued around him.