I could use some help with ideas on the afterlife for a story I'm trying to write in the next 17 days

Before I mention the fandom and thus possibly drive off people who don't like it, the help I need relates to the afterlife, Halloween, related traditions (Day of the Dead, Samhain, any late October-early November festival involving those who have moved on, and such) and has nothing to do with the fandom.  So even if you don't like the fandom please at least read the part that says "this is where I need help" in giant bold underlined letters.

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Since I have three Kim Possible stories going on I'm following the fandom more than I normally follow such things.  Thirteen days ago, on the first, a contest was put out for Halloween themed stories.

I had an idea like this:

At point in time A a villain changes the past (something that happened in an actual episode) so that an instance of Kim teleporting (might be the only one for all I know) goes wrong.

The result is that the entire world changes to one dominated by supercharged decay.  Two characters (Shin and Jacob) are protected from the changes and find that the city they were in is now ruins, mold, rust, rot, and fungus rule.  Lots and lots of mushrooms in all colors of the rainbow some the size of trees.

Since the villain changed the past by means of a magic ritual performed on Halloween, and thus it is that time of year,* protagonists end up contacting dead people* to find out what happened when  time was changed (portal to a bad part of the afterlife was opened, evil has been pouring out for a quarter century.)

End up creating a time machine to try to go back and fix things.

Point in time B looks like but a moment from Earth's perspective, but it's much longer from Kim's while she is dumped into the bad part of the afterlife.  She has to make it back out, through the portal (already opened) which is difficult because of death incarnate things.

Point in time C is earth immediately after the change, a scraped scarred and bruised Kim has appeared shellshocked next to the exploded wreckage of a fax machine (teleportation method used the phone lines, you needed to dial a phone for it to work) that is a slowly expanding portal to bad part of the afterlife.

People try to stay alive and fight back against the bad shit flowing out of the portal.

Story tells all three of these stories simultaneously by jumping between them.

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This is where I need help: What should bad part of the afterlife look like, what should be the evil army that's transformed at least part of the future world into a dead except fungus, mold, and other representatives of decay place.

What are some Halloween related ideas, concepts, tropes, whatever, that I can call on in the service of the story?  (Day of the Dead and Samhain stuff can totally apply.)

Here's the beginning I've got.  See how I stalled just as I needed to describe who/what bad guys are?

Other than contacting dead souls to get information, and the toadstool people (a group of my own invention) I don't have any solid ideas on good afterlife/decay stuff, to bring into the story, and I have no idea what the bad afterlife/decay stuff should be even though that's what drives the entire plot.

Help.

Please.

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Jacob was wiring something together from components he'd ripped out of cellphones. With the boss he never found himself this bored, but with the boss taking time off for personal reasons, and him needing to stay in fighting trim to be able to fulfill his duty when she came back, he'd been hiring himself out to lesser lights of the villainous world.

With them he felt like the great Shego, before she switched sides, if she'd lost her nail file.

So on the way over he'd picked the pockets of some rich kids, stripped their phones down to the bare essentials, and was now making something. He didn't know what, she didn't care, at the moment he was maximizing power and reception, because those made sense when you started with cell phones, after that he'd probably work on transmission strength.

If you just did what came naturally, you could actually make a lot of progress on a project before you knew what the project would be.

It was certainly better than listening to the slob who passed for his current employer drone on.

Mancer was nothing like the boss. He was an nth rate villain who didn't even know that the suffix "-mancer" meant seer, as in a prophet or oracle, not "mage" or "magic user" in general. The man couldn't even get his own name right, how could he possibly hope to accomplish anything?

If some hero didn't show up to stop Mancer soon, Jacob thought he might scream. But he concentrated on the device he was making as a way to keep hold on his sanity.

Then the door exploded inward, and there was a distinctive green glow amid the dust and debris of the shattered frame. Jacob smiled. This was why he took the job. He could in fact care less about Mancer's money, but not much. There simply wasn't that much space between the amount he cared and absolute apathy for the caring less to take place in. No, he needed practice, and whichever one of them it turned out to be, Jacob was sure he'd get that.

* * *

Shin walked into the room, a very sparse underground lair mostly in brushed concrete, and saw the stolen relics on a central table arranged for some kind of ritual, already in progress from the looks of it. She also saw her arch nemesis, Jacob, quickly shove something into one of his coat pockets.

"Starting to think you're following me, Possible," he said. "How did you even know I was here?"

It was half true. When she'd heard about the artifact theft she' figured the local authorities could handle it until she found out Jacob was in the area. She wasn't going to throw local cops in the path of her arch nemesis even if this whole thing did seem like it was beneath his pay grade and her notice.

Still, it was only half true, and she wasn't about to feed his ego. "You think too highly of yourself," she said. "I'm here for those," she pointed at the artifacts.

"Those trinkets?" Jacob asked in obviously fake surprise. "Besides, I thought you brought your girlfriend along on occult missions."

"She's taking some children trick-or-treating," Shin snapped.

"That sounds very responsible of her," Jacob said. There was no jab there, just a simple statement, but Shin knew an attempt to throw her off her game was coming.

"I was looking forward to spending tonight doing that with her but somebody--"

"Has to be the grown up in your relationship," Jacob said, "so when the call came in she stayed behind to be the responsible one while you came out to play. I get it now."

Shin had been planing to that somebody had to go and break the law on Halloween. He made it sound like she wanted to be here instead of with her girlfriend. She was through with the verbal stage of the fight, she tossed a ball of plasma in his direction.

* * *

A key factor in any fight was maintaining an awareness of your surroundings, otherwise you could dodge right into a wall, deflect a blow into a multiphase tachyon transducer, or step right off a cliff.

It was in the course of doing so that Jacob noticed something.

"Time out," he called to Shin.

Once he was sure there wouldn't be any plasma coming his way he addressed Mancer.

"The elder Possible looks pretty young there," he said pointing to to a hole in reality itself, hovering in the air, that showed the spot in space and time Mancer intended to affect.

Mancer didn't respond to Jacob and instead continued reciting an incantation that he erroneously thought was in Latin.

"I hope my real boss rejoins the game soon," Jacob said to Shin, "freelancing sucks."

"My heart aches for you," Shin said in perfect deadpan.

"You have any idea regarding how long ago that is?" Jacob asked Shin.

"That's the transportulator," Shin said.

"Dr. Dementor's hardline transporter?" Jacob asked.

"Yeah."

"Drakken tricked your mom into stealing it because she's so very easy--"

"Yes."

"Caused no less than sixteen people to become convinced we were living in the Matrix?"

"Yes already!"

"When did your mom deal with it?" Jacob asked.

"High school," Shin said. Jacob's eyes went wide. "Near the start of junior year."

"Mancer," Jacob shouted, "You can't mess with 2004! I won't even be born if you screw up that part of the timeline!"

Mancer did finally look up. "That's of no concern to me, I was already around."

"You think you'd be the same person with more than twenty years of your life swapped out for those in the new timeline!?" Jacob shouted, "You'll annihilate yourself and turn your life and body over to someone else!"

"I'm protected," Mancer said.

When a ball of plasma exploded against an invisible ball that, Jacob estimated, was centered on Mancer. Jacob did the only sensible thing. He flinched back and raised his arms for protection.

"Warn me before you do something like that," Jacob shouted back toward Shin, then he turned to Mancer again, "You think a magical shield is going to save you from changing the entire damned timeline?"

"No," Mancer said in a condescending way. That was good, condescension could lead to explanation. "Whosoever takes one of the thirteen malachite amulets from the sacred urn," Mancer said gesturing at a skyphos, which was nothing like an urn, "is immune to timeline changes."

The skyphos was inside of the invisible bubble, Jacob couldn't reach it. Besides, he had a different question, "Why thirteen? There's just one of you."

"Feeble minds such as yours cannot hope to understand the complexities--"

"The spell called for a full tribunal, didn't it?" Shin asked.

Jacob turned to Shin and didn't hide the confusion he was feeling.

"A tribunal is composed so that it has one and only one member who was born in each of the lunar months," Shin explained.

Jacob nodded. Thirteen months in a lunar year.

"If it was intended for a tribunal it means that they thought anyone attempting to do it on their own was dangerously stupid," Shin said.

Mancer snorted like any half-rate villain who'd had incompetence exposed, and then said, "You clearly don't understand the--"

"You weren't smart enough to modify the spell into a single practitioner affair," Jacob said, "so you took the much easier shortcut of tricking the spell into thinking there were twelve other people and then preformed it as originally written, right?"

"You served your purpose," Mancer said. "You distracted her until the ritual itself protected me and now nothing can stop it. See!" He pointed at the hole in reality that was a window through time. The image of Kim Possible dialing the telephone number of her school in preparation for using the transportulator flickered, then she was shown to have dialed a five where in the original timeline she'd put in a six.

Jacob was confused.

"That's it?" Jacob asked. "You've summoned power so great it threatens to tear the universe asunder and all you did was change a six to a five?"

"Don't underestimate the little things, my former employee," Mancer said.

"For want of a nail?' Jacob asked.

"Nothing so subtle," Mancer said, cruelty in his laugh.

Shin turned to Jacob, "What if the changed number was a cellphone number?"

A look of horror passed over Jacob's face. There was a reason that the transportulator was hard line only.

"Nothing so provincial," Mancer said.

Mancer grabbed one of the malachite amulets from the skyphos, then disappeared in a puff of something Jacob was pretty sure wasn't logic. The world around them started to warp and twist.

"Grab the malachite!" Shin shouted. Jacob lunged, taking on faith that the magic shield had disappeared with Mancer, and got a piece just as the last remnants of the spell collapsed into nothingness.

The room went dark.

* * *

Jacob coughed somewhere to her right. "That is foul," he said.

Shin agreed. The air, which had been fine before, now made her want to retch and her stomach churned with every breath she took.

Shin lit her right hand. The green glow showed a largely unchanged lair, the walls were where they left them, the ten remaining malachite amulets were where they'd fallen when

"Show off," Jacob grumbled, looking at Shin's lit hand. Then he reached into one of his pockets, rummaged a bit, and finally removed one of hisimprovised inventions. When he put it on, a small illuminated disk was held in the palm of his hand. When he activated it, which he did in spite of it having no obvious controls, it became a flashlight, shining out in electric blue.

"Now who's the show off?" Shin asked, but Jacob seemed more concerned with what he was seeing.

Shin looked around again, with the added light from Jacob.

Every surface seemed to be covered in mold, explaining the foul air, and mushrooms had grown through cracks in the floor and walls that hadn't been there before. What little wood there had been was rotted. Metal rusted.

It got worse from there.

"This whole place is drowning in decay," Shin said.

"Let's get out of here," Jacob said, "before we inhale something we'll regret."

"I already regret it," Shin said.

They were nemeses, but they'd worked together more than once and, as long as neither of them acknowledged camaraderie, it shouldn't complicate their relationship too much to do it again now.

Shin collected the ten other amulets into a pouch, and followed Jacob out of the room.

* * *

Jacob heard Shin emerge from the remnants of the building, walk over the same rubble he'd come over, and finally stop beside him. He barely registered any of it.

"This was a city when we went underground, right?" Shin said.

Jacob surveyed the wreckage before saying, "We'll want to look for new construction--"

"Less than 25 years old," Shin said, "or thereabouts."

"Exactly," Jacob said, "What changed after he changed time."

"How could one digit change all this?" Shin asked.

"Your mother was teleporting," Jacob said. "Where she went, we don't know. What she found there, we don't know. How, if at all, she made it back, we don't know.

"You think she brought something back with her?" Shin asked.

Jacob nodded.

"Something from elsewhere."

Jacob nodded.

"Then the question becomes, what could have done all this?" Shin gestured to the remains of the city.

"I don't know," Jacob said as he looked around again, "but I haven't seen chipmunk or squirrel or heard a single bird chirp, since we got outside."

* * *

"You think everything's dead?" Shin asked. Fungus seemed to rule the city, so something lived. A tree in the distance looked alive.

"At least it's colorful," Jacob said.

Bright orange fungus, white fungus, red fungus, bright yellow fungus, a bit of pale purple fungus. A fair range. It was colorful. But that was hardly the point.

"Forget the scenery," Shin said, "Just do your mad science thing and--"

"Angry science is seldom good science," Jacob said.

"You know what I mean," Shin said, "just--"

Something moved in her peripheral vision.

"What?" Jacob asked.

"Did you see--"

Something else moved.

"Saw it," Jacob said. "Back to back?"

"Yeah," Shin said. Jacob pulled his hand-flashlight off and pulled out "gloves" Shin had grown to hate. They didn't look like much: wires connecting various small panels, mostly disk shaped, which seemed to be Jacob's preferred format. The disks at the palms didn't look all that different from his flashlight.

The gloves had two main functions. One wouldn't matter as Jacob didn't have his hover board. The other was that it allowed him to catch and redirect her plasma. It was like the xistera hand mods on her mother's battle-suit, but worse.

Shin couldn't see Jacob's hands, one of the down sides of standing back to back, but by the time Jacob's shoulder blades touched her own she heard the soft hum that meant they were active.

"Pass me ammo?" Jacob asked.

In each hand Shin formed a plasma ball the size of a softball, then shot them straight back.

"Thanks," Jacob said.

"I don't like that they're not letting us see them," Shin said.

"That's what worries you?" Jacob asked.

"If we don't know what we're facing, we can't form a plan," Shin said.

"Which is why it's an unremarkable tactic to keep an enemy off balance," Jacob said.

"So what's got you worried O' great and smart evil one?" Shin said with what she figured was just enough contempt that it would let Jacob know how she felt without damaging their ability to fight as a unit.

"That they're swarming," Jacob said.

Shin hadn't been paying attention to that. She'd been trying so much to get a clear look at one of them that she hadn't noticed how much movement she was picking up in unclear looks. Bodies mostly hidden by what used to be buildings, or behind tree sized mushrooms and assorted other fungus. Non-stop motion the periphery --the one place neither she nor Jacob would be able to get a clear look.

"Unless you're planning on repeatedly stopping during combat to give me fresh plasma," Jacob said, "I've got two shots before I'm close combat only." Shin nodded even though she knew Jacob couldn't see it. "I don't like the idea of letting that many opponents get close."

"Getting soft?" Shin asked.

"You wish," Jacob said.

Then the charge started.

They came from all sides and rushed the hero and the villain.

When Shin saw how they looked, she said, "If they wanted me off balance they should have let me see see how they looked from the start."

Jacob responded with, "Given that they look like that."

Four shots of plasma were fired, and the battle was joined.

* * *

--------[date in the past]--------

"It really does work like a phone," Kim said. She dialed the number for Middleton high school back in the US. There was a ring, then a high tone, then a trilling tone, and the world was gone.

When Kim hit the ground she was moving forward fast, even though a moment ago she'd been standing still.

The jagged ground scraped her before she came to a stop.

"Dementor must not have ironed all the bugs out," Kim said as she got to her feet. As her eyes adjusted to the darker lighting, she realized that she was in a cavern of some sort. Some other part of Drakken's lair?

If it was, it was a part he hadn't been using. There was no sign of human activity anywhere,

-

And I stall more or less there.

Some scenes for the future in the future:

On getting help from dead people:

Shin: We need to get the lay of the land.
Jacob: Civilization collapsed, decay has been turned up to an absurd degree, and we're hiding from demons in a grove of bright orange mushrooms.
Shin: We need to find out what happened after he changed time.
Jacob: Well everything I might make a time viewer out of rusted, rotted, corroded, eroded, imploded, collapsed, or decayed so--
Shin: Let's hold a seance.
Jacob: Because that makes sense.
Shin: It does! We could get living witnesses to the altered timeline.
Jacob: Your proposed living witnesses are dead.
Shin: You know what I mean.  Besides, do you have a better idea?
Jacob: I hate you sometimes.
Shin: Just sometimes?
Jacob: There's a reason we only ever team up when the fate of the world is at stake.

On the ethics of time travel

Girl in altered future: Who are you?
Jacob: We're villains.
Shin: We're not.
Jacob: We are horrible, horrible people.  We're the bad guys.
Shin: We're the good guys.
Jacob: So when circumstances force me to be good it's ok for you to be all, "You're a hero at heart," but when they force you to be bad I don't get to gloat?  Double standard much?
Shin: I'm not being bad.
Jacob: (to girl) We're planning on destroying your entire world and replacing it with one that appeals to us more.
Shin: No we're not.  We're planning on setting things right.
Jacob: By which you mean restoring the original timeline and thus erasing this world from history.
*pause*
Shin: (to girl) We'll get back to you.  (to Jacob) Talk with me a minute?

In the end they'll be trying to save no less than three different earths.

-

* October 31st = Halloween - the day we wear costumes to keep nasty spirits from hurting us
November 1st = All Saints Day - the day for dead saints
November 2nd = All Souls Day - the day for dead everyone
All of the above = Days when the border between life and afterlife is thinner than usual