What do you mean?

undead or coming back from the ashes to live again...im a phoenix

Oh. Then thanks for that :3

The episode "Video Makers" mentions the war when they see the copyright on the movie. There are also references like a nuclear bomb right at the beginning of the theme song by a dead tree. There are many other references to keep your eye out for, you just have to pay close attention(not gonna list 'em here cause there is quite a few).

There are also a few item references in some episodes. I will post a quote from the wiki on some of them here:

¡Adventure Time Theme Song: An opening shot showing various weapons and technological debris, including grayed land and undetonated nuclear missiles lying around like a russian SS-13 ICBM, and an arm reaching upward (most likely a zombie) in a tree trunk. The bashed up television is just another remnant from old Earth.
¡Tree Trunks (episode): Traffic signs, which have since somehow mutated into Sign Zombies. It is unknown how this has happened. The painting in Tree Trunks' house looks like it could be Egypt due to the triangular structures it shows that may be pyrimids.
¡The Enchiridion (episode): When Finn and Jake first walk through the forest of Mount Crackdor, pieces of metal can be seen as they look for the sacred book. Some of the pieces at the top, right corner of the path may be sinks.
¡Business Time: Ancient artifacts frozen in icebergs, including computers, a bike, baby shoes and the Businessmen. Finn also uses a flamethrower built from two fuel tanks connected to a rifle by a tube. When the Businessmen, along with Finn and Jake, are shot up into the sky, they fall back down revealing the entire Land of Ooo. Ooo seems to be a large island, with open ocean surrounding it.
¡My Two Favorite People: When Finn and Lady Raincorn confront Jake and Tiffany, the bottoms of upturned cars can be seen in the ground. Jake also uses a military issue phone and headset.
¡The Witch's Garden (episode): The remains of a highway system and a plane's wing can be seen near Gary's nest; the River of Junk is essentially a river of mundane pre-war artifacts. Near the River of Junk, a car door can also be spotted close by.
¡Ocean of Fear: Underwater city ruins and vehicles appear, and a brief scene shows a damaged aircraft carrier and a stranded tank- an even briefer scene depicts two dead bodies on a couch in the remains of a pre-war living room. Finn and Jake also take to the depths in a submarine. You can also see the remaining tops of cars while they
Two dead people on the couch in a pre-war living room (Ocean of Fear)
Added by Mistocerousare floating over what might have been an ancient road.
¡City of Thieves (episode): When Finn and Jake are in Penny's tent, a double barrel shotgun can be seen sitting among a pile of gold coins. In addition, the stolen chest of coin from the tower contains a cell phone in the bottom left corner.
¡What Is Life?: NEPTR is made from an old microwave, a device used by former civilizations from the past.
¡Finn Meets His Hero: In Billy's cave, TVs, a bathtub, and other items can be seen lying around.
¡Storytelling: There are many remains of radios and debris scattered throughout a forest. The young bear is also spraying graffiti on what looks like an overgrown van.
¡Power Animal: A broken TV is seen beside the trunk of Finn and Jake's tree house when Jake walks up to the water girls.
¡The Other Tarts: Various boats and whale skeletons can be seen in the Desert of Doom, suggesting that it may have previously been a body of water.
¡The Silent King: The storyboard[1] for "The Silent King " contains the first time The Mushroom War is mentioned by name in the series, heard when Gummy is reading from the rule book. However, this line was cut from the actual episode. The overturned auto mobile that appears during the goblin riot also is another artifact from past civilizations.
¡The Real You: A shot of Earth appears, and a huge chunk of it is missing. The missing piece of Earth could have been a result of the Great Mushroom War.
¡Death in Bloom: Debris of civilization, including numerous police vehicles, in the Land of the Dead. There are also crashed UFOs, possible hinting technology when the apocalypse happened was very advanced, or aliens. (UFOs were seen in Her Parents as part of the Rainicorn-Dog Wars but it is unknown if it is from that, and in the episode, Mystery Train, a poster on a passenger car reads "Watch Out For UFOs") They also take an escalator down to the Entrance to the Underworld, and a TV is in the ground when they "sneak" past the entrance.
¡Susan Strong: The Hyoomen Tribe live in the ruins of an underground city. In the underground city, a car, a refridgerator, and some sort of submarines/huge ships can be noticed. In the storyboard, a warning reading "Biohazard Danger" appears on the hatch, although this was cut from the episode.[2] The inhabitants were possibly humans driven there during the war and later mutated. Also, in one brief scene, the camera pans over a pile of junk. Upon closer inspection, one can see what apears to be a robot/mech arm sticking out of the debris, suggesting that perhaps robots/mech were used during the Great Mushroom War. There is also what seems to be the front of a tank sticking out of the garbage when Finn and Jake first jump down the hatch. Looking even closer, you can see artificial UV lights strapped onto the pillars, suggesting that the underground city may be, in fact, an underground "bunker city" of sorts where the humans would survive while the war waged on above their heads.
¡Go With Me: The Drive-In Theater houses the remains of many aged cars.
¡Belly of the Beast: The remains of a damaged car rest in the throat of the monster as Finn and Jake return to confront the bears in the stomach.
¡Video Makers: Video cassettes feature movies such as Heat Signature that were made prior to the war. Jake even mentions the Mushroom War in the episode. Similar video cassettes and VHS tapes appear again as tapes of the Ice King's diary in the episode, Holly Jolly Secrets. The fact that Finn and Jake say they see the FBI warning on all the movies they "dig up" further explains past civilizations.
¡Mortal Folly: The base of The Lich's power is a disrepaired, ruined subway station with deserted trains and littered with human skeletons scattered on the floor as if they had been killed that very moment around the station. The Lich gets it powers from "Toxic Waste". Character designer Andy Ristaino has stated that these skeletons "were supposed to feel like they were east coast commuters ... all bundled up for winter."[3] Outside the station is what appears to be a nuclear missile. There are also ruins of buildings in the background.
¡Mortal Recoil: While it is unknown where they would get them, Jake implies that the Lich's "Well of Power", which he recreated in Princess Bubblegum's bathtub with various chemicals collected by Finn, is a vat of toxic waste left behind in his former lair.
¡Heat Signature: The title card shows Finn and Jake standing on a tearing, fading billboard (Finn eating a sandwich and Jake spray-painting a picture of Lady Rainicorn) which stands in a destroyed urban background. In front of Marceline's Cave there is a defunct highway that acts like an awning. There are also the remains of an old car across from the cave entrance. Later, the ghosts take Finn and Jake to the top of what looks like a torn up skyscraper with a helicopter crashed on the roof. The skyscraper does have a helicopter "H" pad on top, and other tall buildings can be seen nearby.
¡Memory of a Memory: Many of Marceline's childhood memories appear to be around the ruined remains of civilization: she is seen as a little girl living in a ruined city with a derelict tank near her home, then later catches her father eating her fries at a destroyed diner. This could be the fallout of the Mushroom War, which could cause a continuity problem, or it could be wreckage from a previous military conflict that eventually escalated into the Mushroom War. In Marceline's memory of a little girl, the unknown city in the background can be seen on fire. Around Ash's house, there are many tires and other debris strewn about the area. There is also what appears to be a mobile home on the roof of his house, which has an aged tow truck balanced on top.
¡Hitman: Outside the Breakfast Kingdom is a desert with an abandoned railroad car near it, also a sewer pipe leaks out water for the moat around the castle.
¡The Monster: When Finn and Jake find the villagers, various metal tools are on the ground.
¡Wizard Battle: The arena for the battle seems to be a broken down football stadium. Also, when the sun sets, in the background, there can be city buildings and towers from modern times in the overgrowth of the forest.
¡Legends of Ooo: a game on cartoonnetwork.com, mentions the Mushroom War. If you click on the radio in Marceline's house, Jake states that, "They stopped making these before the great Mushroom War."
¡The Creeps: A portrait of what appears to be of New York City's silhouette.
¡Beautopia: Beautopia appears to be the ruins of a luxury resort, as seen in the title card. When Susan , Finn, and Jake arrive at Beautopia, it seems as if it was some sort of mall or luxury resort due to signs left on the sides of buildings such as "Eat", "Sale", "Buy" , and "Food".
¡Thank You: Outside the home of the Snow Golem appears to be a snow covered bulldozer, which could possibly be an artifact from before the war. The house in which the Snow Golem lives could also be a remnant from before the war, as suggested by Tom Herpich's promo art for the episode, which depicts a family of humans (or humanoids) living in the house in a time before it was covered with snow.
¡The New Frontier : When Finn and Jake see a rocket built or found by Banana Man , Jake states that rockets haven't been re-invented yet when Finn is worried he might die. This (and the acedemic worms talking about Nietzsche's Ubermensch, along with Jake's mention of Mozart and Beethoven) indicates that not all knowledge premushroom war is lost. There is also a limousine buried in the ground near the home of the Banana Man.
¡Holly Jolly Secrets Part I: The place where Ice King buried his suitcase full of tapes looks like an old junkyard. Next to Finn was a boat that had a harpoon on the front of it. It was probably used for whaling. A truck, a car, and a small plane also lie near the Ice King and Finn. When Finn and Jake are digging for the suitcase, a shoe is hanging from a tree branch and a TV is seen underground where the suit case was buried. A trumpet is also seen tied to a tree branch above the Ice King.
¡Holly Jolly Secrets Part II: The last tapes played showed the Ice King as a human (Simon Petrikov).The Ice King's crown apparently turned him into what he is now, as seen in the videos. In the first clip Simon is seen in a photograph with a sniper in the background. Outside the window that Simon (the Ice King) is talking by, a city is seen, undamaged. Simon said he purchased the magic crown from a dock worker in Northern Scandinavia, a region of Europe. During his video, Simon states "the power of the crown will save him with its frost." He mentions that he does not know what this means, suggesting that the video might have been recorded right before the beginning of the war. (*A sudden snowstorm is seen to start up outside the window shown in the tapes that quickly blankets the city. This could possibly be an allusion to the onset of a nuclear winter, or the onset of the crown's powers, creating the Ice Kingdom around him.) This may mean that the Ice Kingdom is the city. Simon also mentions that his former fiance, Betty , left him due to his irrational behavior caused by the crown. It is also possible to see a map of the eastern part of the Americas behind Simon in the first part of the video.
¡Marceline's Closet: When Finn and Jake are playing Hide and Seek, ("Cloud Hunt ") Finn sings a song that goes "Over the mountain the ominous cloud, coming to cover the land in a shroud, Hide in a busshel, a basement, or cave, but when the Cloud comes a' hunting, no one is safe!", maybe referring to mushroom clouds created by nuclear bombs in the Great Mushroom War. While they are hiding in Marceline's closet, the Spider that lives in Marceline's wall looks like it has many eyes, big fangs, and somewhat radioactive.
¡Paper Pete: At the end of the episode when Finn and Jake are walking away from the library, one can see buildings rising from the ground surrounding the library. The library itself seems to be made before the Mushroom War, too.

As you can see, there are a TON of refernces to just keep your eye out for. I don't expect you to read all of this by the way haha.

Ok there were a lot of random symbols and junk in that post cause of the pictures and symbols in the wiki that are not on the keyboard, so please forgive me for that long post with a lot of stuff. Again I don't expect you to read it all, just showing the extent of the references.

Ok so I've been holding out on my character so I'll post it now (finally):

Name: Rawrin
Gender: Male
Age: Unknown
Race: Human/Penguin
Background: Rawrin is a human... err, penguin? No one is sure. He has the shape (more-or-less) of a human and the stature of one as well. His characteristics however are of a penguin's. No one knows how he became this way. He wears a hood and cloak all the time, to hide his penguin characteristics. All you can see of his face is his beak protruding from under his hood, unless on the rare occasion he takes it off.

Anyways there is my character. The reason for the human/penguin hybrid is because penguins are my favorite animals but I had to have a way that he could effectively fight and get around. Anyways, I'll try to get the game going soon. Thanks for your patience!

How many characters per person?

Each person only has one character. I'm not sure what you mean pyroboom. I have a char, you have one, and takley has one. That's it. :-/

this is not a video game....

I'm interested in making a character. It sounds fun and I love adventure time!

Do we just use your guide and message you?

I was asking:how many characters can one person have, to RP with. I was thinking of a new character(can't believe that, ), and I realized I already had one. O.K., so one, that character has died in the abyss of OCs(you don't really need to know what that is...)(really)

Haha alright pyroboom I'm kind of confused but ok!

Name: Ice Princess
Gender: Female
Age: 17
Race: Icy (Human)
Background: Found by the Ice King and he decided to turn her using another crown artefact he had found (when he was still human) and she had amnesia from surviving radiation. She left him when he captured all of the princesses in ‘Prisoners of Love’ before Finn and Jake arrived.
She created her own Ice Kingdom after that and sits in her palace with ‘Pink the Kitten’ (Gunter’s abandoned floating cat child). She looks like a young Ice Queen.

Name: Henry
Gender: Male
Race: Human
Background: Henry is a warlock. He lost most of his memory after his floating tower exploded. He's around 15, a little hyper, kinda childish, and can't see further than 3 feet due to reasons he cant remember. Since the tower explosion he has been wandering around the lands surrounding the candy kingdom with a floating eye he summoned so he didnt bump into things (even though it didn't do its job very well).
Description: Short messy brown hair, brown and purple robes that are a little short, brown boots.

We are tot's at 5 people! I am hoping I can get the game up by the end of the month at the very (very) most. Thanks again and again for your continuing patience!