Scribblenauts/WMG

Maxwell is in the afterlife.
And his main tool? For all intents and purposes, it's an ultra-strength Death Note Everything Note, pulling whatever he needs from the various multiverses. (If you find yourself in Maxwell's presence, try not to die.)
 * ...Time machines can die?
 * It has a very loose definition of "death," including "vaporized," "broken beyond repair," and "hurled into a black hole."
 * What about black holes themselves?
 * Black holes can evaporate... the term "Hawking radiation" comes to mind, but I Did Not Do the Research, so it may or may not have anything to do with it.
 * But that mans I killed a bunch of exploding Amazons and then Deader Than Dead killed them.

Maxwell is a young god.
He has the power to change and influence the world around him in nigh-omnipotent ways. He can even control other gods! However, the other gods in the Pantheon have set up a course of trials for him to see how well he can wield his godly powers. If he makes it, he becomes an Overdeity.

Maxwell evolved from Finn.
Look at them! Similar shirts, similar shorts, similar backpacks... the Rooster Hat clearly "grew out of" Finn's hat.
 * So... that makes Finn a Pokémon?

Alternatively, Finn evolved from Maxwell.
Finn is a flawed clone Maxwell tried to create using his notebook.

Maxwell is Dark Yagami's Shinigami form.
What do you think his notebook is?

Any bugs or downsides to the game were left there intentionally.
Because otherwise, they would have created a game so awesome, it would have been unsafe for the average human being to handle, and too dangerous in the hands of sinister minds capable of properly wielding it.
 * Alternatively, Maxwell is playing in a Garry's Mod take on The Matrix and all of the glitches that he encounters are imperfections in the render.

Maxwell is a Reaper-in-training.
He has a special ability, which is to make noise by attaching Soul to his drawings instead of attaching it to pins. As a result, his Noise look more like normal objects than other Noise. He can summon anything he wants, but because he's still a newbie, he can only make so much Noise before he has to erase some of it. He's collecting Starites because it helps him improve his Noise-making abilities, increase the amount of Noise he can create at once, and also helps him think outside the box.

Scribblenauts is a recruitment tool for the Green Lantern Corps.
A la The Last Starfighter.

The next time Sinestro attacks Oa, he'll be fended off by an army of Longcats.

Maxwell is on a Mad World-esque television program.
Rather than killing each other, the contestants are put through various arbitrary puzzles. The show-organisers have supplies of everything available for all contestants: Maxwell's scribble-pad is merely a device for communication with the suppliers. 'ollars are the prize money, which can be spent on music off iTunes and plastic surgery (avatars).

Spiral Energy powers the notebook.
Creates things out of nothing? Yes.
 * But it can only create a single variety of drill, and its a dinky little one! And it can't make any giant pilotable mecha!
 * However, that dinky little drill can pierce the heavens in very few hits! You can also summon Bear Curry.
 * Only a "single variety"? Try typing in "pneumatic drill." Looks more like the kind we know, even if Maxwell uses it like a shovel...
 * Actually, that's a jackhammer. Seriously. It gives the same result as "jackhammer".
 * While you're at it, type in "mech".
 * Or a "mecha".

Maxwell is merely the projection of something from a bizarre otherdimensional reality.
He has no power of his own, and is instead the projection and focal point of something vast and incomprehensible, possibly a god. The world of Scribblenauts was conceived of and built by such creatures, deliberately designed to crudely mimic a vastly simplified version of their reality. They amuse themselves in this world by summoning things and creatures in order to collect Starites and accumulate ollars, both things that are utterly valueless to them. They do this purely for amusement; this lets them play in other places in the world, lets them transform Maxwell into things like ninjas and brides, and allows them to change the very soundtrack of reality.

Occasionally, when something that has been summoned is being repositioned in and out of "real" space and not-quite-reality, Maxwell will dash toward that site, frequently hurling himself to his doom. He is attempting suicide while the creature working through him is distracted. He's the only one who knows the truth of how shallow his reality is, but like everything else in his world, he has no concept of meaningful communication, and has long ago given up on trying to explain with "Defend", "Follow", and "Spooked". Long ago he was chosen or created to be the one the otherplanar creatures acted through, and so he is controlled directly by them, has no need of or desire for food and no fear of summoned things, and may appear in ridiculous clothing.

There are no real Eldrich Abominations or gods in the world of Scribblenauts. Cthulu is merely a large, tough beast. God is just a tough, powerful human. The true gods and otherplanal creatures are the ones controlling the world through Maxwell, their avatar. One by one they become interested in the world, amuse themselves in it for a while, and then tire of it and leave it to its own devices. The inhabitants who know the truth can only hope that they will never return.
 * The whimsical nature sounds a lot like Superman's Mr. Mxy.
 * Or Haruhi.
 * Yeah, that's us. We are the Eldritch Abomination. So, I guess this is a literal Humans Are Cthulhu.
 * Supporting evidence: the "hostile" nihilist isn't hostile to Maxwell. I don't know what that proves, and I'd rather not find out.

The BULLY was abused by a PRELATE.
In the vending machine level in world five, the bully will attack any PRELATE you summon to the exclusion of everything else, even money. Religious authourity is clearly a Berserk Button. Kids who are abused ofter have trouble relating to their peers, and may develop social disorders like bullying. Alternately, he just went to Catholic school and had a really strict teacher.

Scribblenauts: The Online Multiplayer Adventure
That is all.

Scribblenauts takes place in Chalk Zone.
Maxwell is either a descendant of Rudy Tabootie, or he was able to get his hands on some magic chalk. Either way, it would explain why every thing he writes comes to life.

Maxwell is a younger version of Steve.
Over time, the notebook lost its power as Steve got older. Now powerless, it's the Handy Dandy Notebook. It explains why the world is so colorful, anyway.

Maxwell is a Scribblenaut in training, and that's the plot.
The Scribblenauts are an alien organization (or perhaps a future Earthling organization) who must have Starites to use as fuel for their technology. Starites are a limitless power source, and they never run out -- if you know where to find them. They can be hiding in levels, or can appear when a task is fulfilled. Maxwell is a wannabe Scribblenaut and kept sending letters to them. The Scribblenauts replied back and said that he can be one if he passes the Scribblenaut Test. Before taking the Scribblenaut Test, he had to go to Scribblenaut University. The Scribblenaut Test is basically the whole game, and in it you have to master getting Starites in many different situations. Once Maxwell got 100%, he receives the Scribblenaut avatar, and gets to live out his dream as a full-fledged Scribblenaut.
 * Alternitavely, Maxwell is already a Scribblenaut; completing the tutorial and becoming "a true Scribblenaut" is represented as graduating from university, and the rest of the game after that is one big test meant to help him gradually hone his skill (puzzle levels) and creativity (action levels). Getting 100% completion grants him the rank of Super Scribblenaut, and exploring his newly-gained powers (ex. the ability to use adjectives) will be the premise of the sequel.
 * What's the opposite of Jossed? The devs have said in interviews that this was basically what the plot of the game was before they said "screw it" and just made it fun and random.
 * The opposite of Jossed? I'm not sure. I Knew It, maybe?

Maxwell is a robot.
Zoom in on the sprite and you see screws in him. He doesn't need to eat, does whatever you want, and has no qualms about chainsawing kittens. That is all.

Scribblenauts are Psychonauts.
You can move objects around without touching them. Telekinesis.

Maxwell is in a coma.
Maxwell is, is fact, a perfectly ordinary 10 - 12-year old kid who was injured when the space museum he was visiting blew up. That would explain the starites; many comatose dreams are caused by whatever activated the coma/useless bits of info in the person's head. Scribblenauts is a dream; Maxwell is actually lying in a hospital bed on life support and an IV. At the end of the game, he wakes up. It HAS to be a dream; how else would all the impossible things happen? The doppelgangers are just the acknowledged bad parts of Max's personality that he realizes he needs to fix.
 * So basically, it's all over again...

Maxwell's clone caused the Bad Future in the sequel.
By, you successfully avert the bad future and the game has a happy ending.
 * On the other hand, it could be Maxwell himself who causes the bad future through rampant rewriting of reality.

Maxwell is a Time Lord.
Maxwell doesn't write stuff in his notebook to make them appear; the notebook is a TARDIS that is so much Bigger On the Inside that it can hold millions of copies of everything imaginable. Maxwell has no need for the TARDIS in time or space travel because he has time machines and teleporters, so all he really could need it for would be to get more stuff to put in the TARDIS. This is the whole point of the game: playing as Maxwell in his endless quest to get starites to have more stuff in his TARDIS.

Scribblenauts is an organization that helps people in need.
There can be little other reason for some of the levels. Puzzle levels in the original are missions where you go out to help people, and get starites and ollars for this help, and Action levels are training tasks. Merits are bonuses given by your bosses for your performance. In the sequel, most missions are helping people, while the S-X stages and the levels where, for instance, you have to dress up to impress judges or make connections between different objects, are training tasks.

Scribblenauts have access to a rudimentary form of time travel, powered by starites, and this allows you to replay levels, the first starite powering all further attempts.

Missions take place across an infinite number of alternate universes and timelines. The Playground is just an area inside the Scribblenaut facility where Maxwell plays God in between missions, and Custom Levels are small pocket universes where Scribblenauts can create their own challenges to test each other.

Maxwell has Biggus Dickus.
Put on the birthday suit. Notice how big the censor box is. Notice how it jiggles up and down as he runs around.
 * He's a kid, goddamnit!

Maxwell and the guy you can summon by writing Scribblenaut are alternate universe versions of Kirby and Meta-Knight.

 * Maxwell and Kirby are both kids (maybe).
 * Maxwell and Kirby are both badass adorables.
 * The guy you can summon writing Scribblenaut and Meta Knight both wear masks.
 * And in a few fan comics, the Scribblenaut dude is like a mentor to Maxwell, like how, in the anime, Meta-Knight is a mentor to Kirby.

Maxwell is an apprentice Scribblenaut, and is in a computer simulation where he learns how to use his skills in certain situations.
The "Scribblenauts" are a mysterious organization that can be called for emergencies and other situations where they are required. Starites are required to power the Scribblenauts' notebooks, and Scribblenauts are often required to find them themselves, which is why they appear in the simulation. The reason that adjectives couldn't be used in the original game is that in Super Scribblenauts, a year has passed since the original game and Maxwell has since learnt how to use adjectives. The character that appears when "Scribblenaut" is summoned is wearing the uniform of an fully-trained Scribblenaut on duty. Student Scribblenauts such as Maxwell are required to wear a "rooster hat" helmet, explaining why he wears one. The leader of the Scribblenauts is Jeremiah Slackza, which would explain his cameos in the simulation as an Easter Egg coded on his request.

Maxwell will one day conquer Earth.
The following may seem far fetched. Maxwell was kidnapped when he was a baby during a raid on his village by the Scribblenauts, an evil organisation which harness the power of a notebook which was stolen from the government of Maxwell's planet to create weaponry to scared the government into letting them be the supreme force on the planet, and destroy towns and villages to find new members for the organization. Since he was young, Maxwell was harshly raised in the heart of the scribblenauts HQ, where those who try to escape are killed. After 11 years, Maxwell entered the scribblenaut training program, where he learnt to gain how to gain the trust of the humans on Earth. He spent many years inside the program, and cold heartedly chased down his rival in the program, Llewxam, and caused him to  at the end of the advanced system which included adjectives, code-named "Super Scribblenauts" and emerged from the program ready for his initiation. Once initiated, Maxwell killed the leader of the scribblenauts and became the new leader. In the years to come, he will be plotting his invasion. Someday, he will create an armada and desend into the earth's atmosphere and begin his conquest of our planet. God help us all...

Maxwell is linked to the G-Man somehow
Maxwell is:
 * The G-Man's employee. The G-Man runs the Scribblenaut organization. The Scribblenauts are fighting the Combine Empire, and are trying to liberate humanity and other enslaved species as well as conventional warfare (or at least as conventional has a war against the Scribblenauts could be). Maxwell is a skilled commando agent, advancing several Gambit Roulette, furthering the master plan through is seemingly combat unrelated tasks. Starites are concentrated energy, created by the distortion of reality in a certain way, indicating that the plan will proceed unhindered. Combine leaders, seeing their armies fall at the Scribblenauts' hands, decided to eliminate their enemy's most dangerous commando, destroying morale and stopping the Gambit in it's tracks. The Doppelganger is an attempt to replicate Scribblenaut technology by the Combine, and, more importantly, take out Maxwell.
 * The G-Man's relative. The G-Man's family has a genetic trait which allows them to alter reality.
 * The G-Man himself. Maxwell advanced through the ranks over the years and became the commander of the Scribblenauts. When an exploration team discovered the Combine, the now older Maxwell decided to take them out. He carries his notebook in his suitcase.

Llewxam was a failed attempt at creating a clone of Maxwell for if he died.
It is possible that years before the events that were recorded in the original scribblenauts game, the scribblenaut elders foresaw what was to become of Maxwell and how skilled he would be in the training program. They also realised how useful he would be, so if he died it would wreck their whole operation. So, the go-ahead was given to the scientists at the scribblenaut HQ to create a complete clone of Maxwell so that if Maxwell died, they could release a new copy of him to continue their plans. Unfortunately, the project failed and Llewxam was stored away on a vessel to transport him to a disposal base in the asteroid belt surrounding their homeworld. Llewxam managed to escape inside a jettesoned rubbish disposal unit which, by luck, returned to the planet's surface. Llewxam, upon landing, embarked on a journey to return to the labs and seek his revenge. After years, he made it back and entered the research facilities where he was created. He then proceeded to murder the scientists that sent his to his doom, cloned the bodies so nobody would realise that they had died and finally stole the dead scientist's uniform so he could go undetected inside the base. He then realised Maxwell entering the training program, and transported himself inside the machine as a creatable item. After years of missuse by Maxwell for fun (e.g being used as a target, being eaten by a t-rex etc.), he exacted his revenge by (spoilers begin for Super Scribblenauts here)....

The Third sequel is going to be "Super Scribblenauts 64".
"64" means that you can now have quantities to you words, along with adjectives. So now, I can summon 42 scribblenatical colossal spinning lol cats at once.
 * Jossed, it's called Scribblenauts Unlimited.

Starites are actually barrier cores.
Maxwell is just minding his own business, but when ever he gets close enough to starites, that create a sort of barrier that Maxwell can't leave. Sometimes he can see them, but other times he has to meet certain events in order for them to appear. From there, he could deactivate the starite and go along with his business.

Maxwell's a highly dangourous criminal, wanted By nearly every nation on the planet.
Let's see what type of things are done on a regular basis...murder,thievery, arson, torture,possesion of illegal firearms,animal abuse that includes killing endangered animals, terrorisim and, worst of all, HURTING KITTENS.

Meaning, he doesn't get along well with the authorities.

He accomplishes this using his notebook, of course...But why don't cops/other legal authorities attack you? Easy: Maxwell's notebook creates the items, and isn't aware of the shit Maxwell does, so, it will create things from the point of view that Maxwell is a normal person, causing things to act the way you'd expect them to towards you. (things are hostile,friendly things are friendly.These are NOT things that are sentient, they are "advanced" cyborgs, programmed to react certain ways to certain things in certain logical (Well...most of the time...)ways. Any non-setient item is a perfect copy of said item. (Meaning that 'counterfeiting' can be added to the above list)So, to conclute the logic of his notebook, as I've seem to have gone off-track, cops don't attack you, because they see him as an innocent person, not the crimanal that he that he truly is.

Also, think about the levels: How many have you doing things that would get you arrested/have law enforcement as an enemy? A fair number. And...there was at least one were you were obviously in prison. Who's to say that the first-game level where you had to take down the "Wanted: Dead or Alive" crimanals, you where also an escaped prisoner who just wanted to get rid of the others for your own enjoyment? As for the (much more common) levels where you're just randomly helping out civillians or doing random things,(In a random way. Randomly.)he's being nice to those people who don't know who he is, because he is a nice guy. (I know it goes against what I'm saying right now, but I'll clarify later), and trying to add some more Awesomeness to his life, not like he needs any, though. The random moster invasion levels? You made some zombies or what not to relese into the world and suddenly feel like helping. As for the levels where you help with something goverment related, those aren't real peope like you see in the other levels, those are notebook clones that Maxwell created, too escape the strain of his criminal life, and to convince himself that he's a "good guy."

Oh, and, It gets better: Why would he do something like that? He doesn't want to do any of this. That's right. Based how many different ways there are to play the game, I've concluded that he's little more than a marionette belonging to the player-Except that he can feel emotion, but with no way to express it. All he can do is run and hadle objects. No way to voice his agony as he's burning to death in lava, being mauled by a monster, falling to his doom,or being killed by a nuke, all while the player watches, sometimes laughing, sometimes angered, always unsymphetic. (Plus, he's immortal,meanning that he can experience these deaths, over and over, as many times as the player wants) He has no way to show his terror at the blood of innocents that he's constantly covered in, while the player can't even see the blood though the E10 rating. He has no way to show how sorry he is towards his victims, watching them die painfully, knowing that person views him as the horrible creature you've made him into, knowing they blame him for the actions he makes against his will. He has know way of showing to you the ways you're driven him insane. He doesn't want to be the monster you force him to be; he wants use his powers for good, but the puppetmaster controlling him (read: you) is cruel, and makes him act like a cruel and sadistic person. He knows that he's known as the world's biggest threat...he knows that his hands have shed much innocent blood...he knows you think of him as a simple form of amusement...but he still wants to be a hero to someone. Hence, the Starites come in. Whenever he does something slightly notable, he sees himself as getting one, believing it has some purpose; breaking away from the cruell player,the purification of his overwhelming insanity, the salvation of the universe...they aren't real. They're a hallucination on his part, to help him believe his life amounts to anything. He goes on a quest for personal purification, but only winds up even more broken as a result, thanks to, you, the player, his puppetmaster.

You Monster, indeed.

Maxwell is Mike.
This explains how he was able to summon almost any object he wanted.

Maxwell is playing the Reaper's Game, or at least a variation of it.
The Composer of wherever Maxwell lived when alive like to play the game by his own rules, everyone plays by him/herself, and must complete a series of puzzles within a time limit, failing those puzzles leads to erasement, and to use each's imagination to their fullest, everyone receives a notebook to solve those puzzle, Maxwell is basically a Scribblenauts version of Neku.