This story starts at season 1 for both cartoons. Enjoy!

Grim settled down at the breakfast table opposite from Harold and pulled out part of a list from their robe. "Ah, nothing like reading me list of the soon-to-be-deceased."

Harold blinked, and began folding up their newspaper. "You have a list of dead people?"

"Soon to be dead people." The Reaper flashed a crooked smile. "Want to have a look?"

"Nope, I'm fine! Ignorance, ignorance is bliss." Harold jumped up and quickly walked away, leaving Grim alone. They shrugged and looked back at the list, quietly musing to themselves.

"Hmm... an assassination, that sounds cool. And one dude set to fall off a ladder in five minutes; I wish I could see that!" They sighed. "Now I remember why I don't look at this thing anymore. All these deaths to see, but the last time I paid a visit-"

"Oh Gri-im!" The Reaper's hollow eyes drooped.

"These two kids happened. What is it, Billy?"

"Can you help me eat this tree?"

"Come again?"

"Can you help me eat this tree?"

Grim groaned. "I should have known I heard it right the first time round. Just give me a minute, Billy!"

They looked fondly back at their list. "Those were the good old days. Back when I could personally reap the souls of all the portal accident victims I want, and now- hang on a minute, a portal accident victim?!"

"Grim!" There was a shout from the bathroom. "Get your bony butt over here; the toilet's clogged and I can tell it's Billy's fault!"

"Just a second, Mandy!" Grim stood up, scrutinising the victim on the list. They had less than a minute left to live, but all it said was 'portal accident'. "Come on, can't you be more specific? What's a portal accident?"

"Gri-im?" Billy called. "This tree won't eat itself, hehe! Grim! Grim Grim Grim Grim Grim Grim-"

"Grim, come over here right now. Don't make me use The Watch."

"Not The Watch!" Grim pulled at their hood in despair, looking from the list up to where the bathroom was located. "Argh, just one minute you guys! Forty-three seconds!"

"Get over here, now."

"Grim Grim Grim Grim Grim-"

Finally the Reaper made a decision. Knowing they would regret this later, they summoned their scythe and cut a hole in the air, creating a gateway to the scene of this all-too-intriguing portal accident.

Mandy watched them slip through with a cool glare, and brought up their watch. "Alright, Grim. You're going to regret this."

~Line Break~

"Hang on," Sam stepped forwards and ripped a picture of Jack Fenton's face off of Danny's jumpsuit. "You can't go walking around with that on your chest."

Danny nervously rubbed the back of their neck. "Heh, right." They turned towards the portal. "Here goes..."

The boy stepped into the portal, trailing their fingers along the side, looking around at all the glowing blue lines so heavily contrasted by the shadowy darkness. It did indeed look operational, with not a loose wire or dented panel in sight. Maybe it didn't work simply because there was no such thing as a Ghost Zone?

I mean, that was what Danny and Jazz had been trying to tell their parents all along. But sometimes Danny wondered what it would be like if ghosts actually existed. What if this machine actually worked? What would be on the other side?

As Danny thought about this, their hand unintentionally brushed over the 'ON' button in the portal. A beep brought them back to attention, and they quickly realised their mistake.

Before the boy had time to wonder what kind of person would put an on button inside a portal, the entire machine lit up in a blaze of blue. Danny felt like they were burning from a sudden wave of heat – no, not burning. Vaporising.

They screamed for a long time, even after the agonising pain died away to be replaced by a chilling numbness. They only stopped when they felt a finger poke their shoulder.

"Hello? Hello? Look, I know you just died and all but I'm on a bit of a time limit here."

"Wha-" Danny turned and saw what appeared to be a skeleton in a dark robe, holding a scythe. They immediately started screaming again.

The skeleton rolled their sockets. "Oh, shut up." A watch wrapped around their right wrist bones suddenly lit up green. "And you too, Watch! Let a Reaper do his job for once in a while!"

"Wait, you're the Grim Reaper?" Danny's eyes widened. "Wait, I'm dead?"

The boy held up a hand to inspect. In the swirling green light of the middle of the portal, they saw the jumpsuit had turned silvery and emitted a ghostly glow.

The Reaper laughed darkly, twirling their scythe. "Yes, my boy. I've come to reap your soul!"

Their watch began beeping slowly.

"Wait!" Danny put their hands up. "I don't want to die yet!"

"That's what they all say. Give me one good reason I should let you live." The Reaper cackled, advancing.

"Uh... I'm too young to die?" The boy backed up against one of the portal walls.

The skeleton raised their scythe above their head, their watch flashing red and beeping incessantly. "I've heard that one a million times. Now it's curtains for you, Danny Fenton!"

Danny shut their eyes tightly as the scythe came down.

"Ahaha, hahaha, haha- wait, what? Noooooo-!"

Hearing this, Danny opened their eyes and then gasped at what they saw. The Grim Reaper's scythe was impaled in their abdomen, the point sticking out of his back. For some odd reason, it didn't hurt and the actual Reaper was nowhere to be found.

"Uhhh..." Danny looked around, rubbing the back of their head. "You, um, left something! Hello?"

After a moment, the scythe faded away. Danny stretched and poked at where it had been, but it was almost as if it had never been there. They noticed their glowing hand again.

Weird. Were they dead? Were they a ghost? They barely had time to think about this before they became aware of a voice calling their name from one end of the portal.

It sounded like Sam.