Bobby had warned them he'd never seen anything like it. Castiel told them
It would end their world. They'd charged in anyway. There couldn't be a good reason the creature, whatever it was, was trying to dig through the Earth's crust. Dean had driven while Sam loaded ammo that would hurt anything they'd ever hunted. Bullets filled with Holy Water, Dead Man's Blood, silver and rowan wood shavings.

They didn't leave a scratch on the thing. A gargantua, it was solid black with yellow eyes. The fist was as big as their heads and it's fore arm was as long as Sam was tall. Every time it punched the ground, a pool of darkness formed. Smaller creatures the size of beagles that resembled black ants with yellow eyes. They could knock them out, but a successful kill was beyond their reach.

Then the ground cracked between them. Dean shouted out, falling back as purple lightning fell between black clouds. Sam yelled, and Dean's eyes went wide. The world was vanishing around them. What his tall brother hadn't realized was a pool of the dark goop surrounded him.
"Sammy!" Dean shouted as Sam realized he was sinking into it. His brother began trying to climb out, but he was hip deep. Dean crouched, making a running jump over the gap. He dove, Sam's fingers slipping through his fingers as the younger brother disappeared.
"No!" Dean shouted as the goop vanished. "Sam! No!" He lifted his head to the Heavens.
"Castiel, where the Hell are you? What's going on? Castiel!"

Dean Winchester?

Dean turned. He could hear a voice. As the ground fell away it spoke again.

Don't give up. You'll see him again. Right now someone else needs your help.

A voice was speaking as light surrounded him. It sounded like someone from Star Wars.

"Who are you?" Dean called out.

We'll meet. A laugh as a blade appeared in front of him. There's someone I need you to help until I get there.

"Huh?"

Take the Sword Dean. You'll need it.

Dean grasped the weapon and his eyes grew wide. The hilt and blade became black steel. An emblem shaped like a stag appeared on the hilt.

"Is this...my car?"

You have a strong bond. That will help you.

"Who do I have to help?" Dean cried out, wondering why he wasn't questioning more as he flew through stars, the Impala creating a barrier around him.

Find the Key!