He had no idea how it had happened.

He just knew he had failed.

He felt tears run down his cheeks, along with an warmer liquid.

Blood.

His hand weakly fell down, landing on the hard edge of the cliff.

He wanted to cry out, but who'd hear him?

This was his fault.

His fault.

He couldn't save him.

The Pines' family had finally gotten used to their former enemy living with them, Bill Cipher.
Though Cipher weren't really much of a threat at the moment, he had lost all his powers except for levitation, and that skill he could only use on himself.
Oh and he was human.

Dipper Pines didn't really understand how that worked, apparently Bill had been tricked into a human form, where he then had gotten stuck.
Even the all-knowing demon didn't know if it were permanent.

In pity Mabel had invited the former-demon to live at the Shack. And now three months later Dipper had decided he could probably trust him.

He were bothered by the demon's constant flirting though, but otherwise he had completely accepted him.

Thus why he had accepted Bill joining him for a mystery trip to a giant cave Dipper had read about in his journal.
Bill's last name weren't 'Cipher' for nothing. He was incredibly talented at deciphering codes.
And somehow he spoke fluent Caesar Cipher, which just didn't make any sense for any of the Pines'.

Dipper had solely invited the demon because of that, because according to '3' the ruins had lots of traps and puzzles, some which required knowing several kinds of ciphers.
While the journal itself had a guide for decoding some codes, it would be a lot quicker for someone who could actually speak the 'language'.

Bill grinned doing the whole walk to the ruins, his Pine Tree had invited him (and him alone, no annoying Shooting Star or Question Mark) to go on a 'Mystery Trip' as the younger twin called it, apparently they included anything supernatural and Gravity Falls.

So basically just talking to Bill was a Mystery Trip.

At first Bill had actually assumed Pine Tree was kidding, but apparently the kid had been completely honest about going on a 'picnic' with him.

Thus they made their way to those 'mysterious' ruins.

The ruins weren't much to speak off, they were apparently led into a giant rock cave, which were full of cracks, it seemed as if it could collapse any moment.

Yet Bill followed the Pine Tree inside, curiously looking at the runes which were engraved in the boulders. The path itself wasn't anything but a tiny space surrounded with rocks, above them sharp spear like rocks were threatening to fall down.

Of course that didn't stop the duo.

Finally they came to a former puzzle, which someone had failed at it seemed.
The road stopped completely, in its place a giant abyss like crack was seen.

Bill kicked a pebble down and started counting.

17 seconds before he heard an echo, "no falling, okay Pine-" he stopped himself seeing Dipper being close to step on a trap-like rock.

"STOP PINE TREE!" His pitched voice echoed already, and in this cave...

He heard rocks move, some pebbles fell down.

But Pine Tree stopped, turning to glare at him. "Sssh!" He hissed, flinching a bit as a bigger pebble fell, making dust appear around.

Bill turned to the path they had arrived at, "Let's get out, this place is gonna colla-"

As called one of the spear-rocks fell right in front of his, blocking the path.
And almost impaling him.

He jumped a bit back, turning to face Dipper.

The platform they were on were barely any larger than the path, small enough for them to walk next to the cliff, but large enough for them to be able to walk around.

Another boulder fell, towards Dipper.

About to crush him.

"PINE TREE DODGE!"

And he did.

The wrong way.

To his left.

To the abyss.

Bill ran towards him, quickly getting down to help him up.
He reached out, getting hold of Dipper's hand.

He cried out in pain.

He hadn't heard the rock, which were the size of his head, fall down.
But it did. It landed onto his back, the sharp sound of bones crushing echoed through the cave.

In his pain his hand had let go of Dipper, who then fell.
The kid shouted, Bill tried to reach out.

Tried to help.

Failed.

Failure.

Can't help.

He kept trying to reach the hand, which he knew was already to far away.

He cried now, feeling his body die.

...

Bill was in his demon form, he floated down the pit, ignoring the tanned lifeless body behind him.

He knew he would not see anything anymore soon.

Yet he used his last energy on getting down.

He wished he hadn't.

A seventeen year old young man with brown hair and a white and blue cap with a pine tree on it was laying on the smooth rocks.

His leg was turned awkwardly back, broken.
His neck was snapped.

Blood was around the boy, but that didn't shock Bill.

Because Bill didn't see it, all he could see were the sharp rock which had impaled the boy.