There's a theory out there that states that the entire anime series takes place in Ashe's Mind, sort of like Jacob's Ladder.

In the first episode, before pokemon are even mentioned, Ash falls off his bike and hits his head. He is knocked into a coma, and does not wake up.
Every character he meets is a metaphor or a creation of his own psyche.

I can't remember all of them, but Brock represents his Libido. This also explains why there is always a Jenny or a Joy in each town. They are the representations of two women that Ash new and had feelings for.

Misty is his animus or feminine side. She is a female companion that he could never be attracted to, because she is actually him.

There's also a theory that Mr. Mime (the one who lives with his mother) represents his abusive father transfigured into a harmless form.

Etc.

The accident with the bike? It put Ash in a coma. three days later he was found and pumped full of painkillers. This is why team rocket became less menacing. The drugs kicked in and stabilized his coma dreams, instead of being terrifying, they became idyllic, and he's able to live out his pokemon master fantasies.

It's also the reason that every time he enters a new region, virtually no one has heard of him, despite his conquests, and why givoanni leads team rocket. Ash has daddy issues, so he put his dad atop the evil corporation, and he just can't picture himself as famous, so he essentially adopts a new identity every few months.

It also explains a few other things, such as how a child can go off on his own in a world full of dangerous untamed animals, and why every pokecenter has the same exact nurse.
Brock is ash's repressed sexuality, he fell into the coma a virgin, and needed an outlet for it. since he can never experience it, brock must never succeed.
To further expand on this, one will note how misty, a tomboy, is another aspect of Ash's personality, his feminine side. the feminine side would obviously be upset at the womanizing side, which would keep a normal human being from acting like brock. This is why she constantly batters him.

I can explain the purpose of any character to ash's mindset within the coma to make it make sense.

It's the same thing as his community. Never experienced anything else, and couldn't at this point. He's only able to imagine landmasses besides his own because he used to dream about going to them and winning tournaments there. Also the reason Joys and Jennys are everywhere - those were just two figures he looked up to in his hometown so he projected them everywhere.
Team rocket is aspects of ash's personality that he has deemed "bad" james implied homosexuality, and jesse's vanity. You'll remember that meowth has the potential for rehabilitation, and doesn't want to be evil, so yet again this fits in with the confli\cting personalities theory.

Their methods of capture become more and more ludicrous ( and physically impossible) because ash is just a kid dreaming these things up.

The worldwide socalism can be explained if you once again realize that this is a dream world, he thought up a safe system of government that would run smoothly and keep the world going, allowing his adventures to work like they do.

Pikachu?

Pikachu obviously represents ash's Humanity, hence the episodes where they get separated, and ash wants desparately to find him, but for some reason cannot. Even team rocket is willing to set aside any differences to work together and find pikachu. They want to steal pikachu ( ash's humanity) and hand it over to his father. They will always be opposed because ash does not want to become anything like his father and no resolution can ever permanantly be reached. however he will temporarily reconcile with those aspects of himself in order to save his humanity from just becoming flat out LOST.
Max came with may, she played the ID with great aspirations, and he played the sensible Ego that "Session". They worked for a little while but ash, being a teenager eventually his sexuality had to come back into play. he kept reinventing himself and eventually Wrote new aspects, but his mind slowly brought back the old ones as a crutch to make the transition easier.
Also, why the elite four?

Why not one elite unbeatable trainer?

Because no person has one single psychological roadblock, and toppling all of them in one go would rend one's minds into shreds. I would assume that if he were ever to beat all four the coma would reverse itself.

Now it's time for Gary Oak.
Gary oak is what ash wants to be. He's wish fulfillment. he succeeded, and settled down to a normal life. ash needs someone to succeed in his world or he won't be able to validate it and will start questioning why he's where he is. it's a subconscious trap to keep him from becoming too aware of his situation. His mind must have figured out that awareness of the coma would snap him out of it, but it would cause major brain damage, so it took something the boy already loved and built a way out for him with it. however ash is too complacent to finally fight his way out of it, and cannot escape. this is why he keeps encountering legendaries, they're his mind's way of showing him he can do great things if he tries, and it's a way to encourage him to push forwards.

Dawn is ash giving himself a chance to love. since he already established misty as someone he's not likely to go anywhere with, he created a new super female, one that was more like him, and less violent all the time. ( you'll note that both may and misty had no tolerance for brock whatsoever whereas dawn seems to try and shrug it off.) Richie and his pikachu were another success story for ash, but he wanted one he could be closer with. One nearly identical to him. One that even used a similar roster to him.

Paul is ash's dark side, one that wants to push on even harder and harder, the part of him that will stop at nothing to escape this coma world.

The reason for the new rivals is that gary settled down, he's living peacefully, and to bring him out of that would be to supress part of ash's wishes.There's no way his mind would let that happen, so his personality fragmented further, producing dark (paul) and light (richie) versions of gary.
Mr.Mime is actually a stand in for ash's father, one that can't abuse him or his mom, because he is a pokemon, a peace loving creature that's oddly humanoid, but that can never hurt a human ( ash's trust is because he was never really hurt by a pokemon, so he sees them all as harmless, whereas in the real world they may be quite feral or vicious ( as seen in the early wpisodes), again falling back to the theory that the only real pokemon are the ones from the first season, and everything else is just further speculation coming from his mind on what new species would look like.)
And the movies?

Ash has been switched to a new treatment, and is adjusting to it, so his mind runs wild, allowing things to become grittier.

He releases them (his pokemon) because his mind is forcing him to let go of them. The second he raises an overpowered team, a tournament comes up, and after fighting his way through it he has to go to a new land for new challenges, but with an overpowered team, there won't be any challenges, and no way to motivate him further, part of ash wants to stay in the coma, and keep journeying.

The other part wants freedom, and to return to his real life, to finally become a real pokemon master. However if he's allowed to keep his powerful team there's no reason to meet and ame new pokemon, he'll lose interest, and the chance of becoming self-aware comes around again. so it's not that he gives them up, it's that he loses them, and unless he's desparate ( like with charizard) he can't get them back. it's basically his mind forcing him to deal with his issues.

Aah the reason team rocket's disguises are always believed. He knows it's them ( on some level), but chooses to ignore it, so he can better himself, in a sense escapist ash is sabotaging idyllic ash. So that there can be more conflict, and hopefully an eventual escape.

Oh there are real animals. But they don't matter to ash's psyche so they don't come into play much. if ash had loved puppies, everything would be about different breeds of dogs, and a dog fighting circuit.

But, as the series goes on longer, we've been seeing less realistic animals and more Pokemon.

Could this be a sign of his mind's deteriation? That, as he's in this coma, he's losing concepts of some animals and machinery and replacing them with Pokemon. It could explain things like electric pokemon working as power generators.

The reason ash went mad/evil:
Ash's father visited him in the hospital, even in his coma world he could hear his father's voice and it drove him berserk.

The filler episodes that don't focus on ash and the gang are ash's mind working through, and humanizing the parts of himself that he demonized. It's a way for him to deal with issues that ash and crew wouldn't touch, because it involves treading ground he himself had sworn not to go near.

So in a way, ash IS team rocket.

A sign that his memory of the old world is slipping more and more as time goes by. The pokeyman realm will be idealized continuously the longer he has no stimulus from the real world. He may or may not be mentally deteriorating (he was always simple), but he is becoming more accustomed to his fake world's rules.

This also explains why their outfits are different from the other team rocket goons.

They're white because they're a part of ash that he may deal with.

everything else, the rest of the whole organization is symbolic of his inability to escape his father. those three are the punching bags of the rockets because they're issues that ash himself displayed and was punished for by his dad.

It would also be a good reason why Paul has shown up at this point, and Ash has been forced to work with him on at least one occasion: It's his mind's last ditch efforts to snap him out of this, to force Ash to actually come to terms that this perfect world is not the best option and he needs to wake up.

The narrator is ash's Higher mind. It's recapping and explaining the progress he's made and the tribulations he will face, allowing itself insight into how best to awaken him.

As I said earlier, team rocket and the episodes they occupy are ash dealing with ground he feels uncomfortable with tackling on his own. James' troubled childhood is his way of justifying his latent homosexuality.

It could be an attempt on Ash's part to humanize Team Rocket as well, as part of his mental healing: Team Rocket isn't really evil. They're just jerk who have hit bad times. As time goes on, they seem to mellow out as well, to the point where the only reason why they haven't outright given up on villainry is "We want to make Giovanni (father) proud of us", a possible desire of Ash's that coincides his "I hate you dad".

Meowth had to talk to be more redeemable and accessible to his other bits of personality.

Evolving his pikachu would have challenged his concept of what his humanity was.

when ash is trading pokemon, it's an attempt to push his own problems away on someone else, however he realizes this and usually trades back failry quickly.

Joy and jenny he knew from his hometown, and they act as a safety net or anchor, allowing him to feel safe no matter where he goes.

So maybe their trying to steal Pikachu (as stated, Ash's humanity) is not only a way to impress Giovanni, but to make him a good man again so that he can appreciated his wife and child as he should have (or perhaps did, at one point). Ash is against this because, consciously, he knows that giving over his heart to someone who has been so hurtful to him and his mother will only cause pain for them both.

Misty's Togepi represent a desire for offspring and a family of his own, or merely an attempt to defang Misty? Because she starts off as rather rageful, especially towards Ash, but after she gains Togepi she mellows out and acts much more motherly (mind you, it's mostly towards Togepi, but it's still a mild personality change)

The pokemon in Ash's team are his issues, for example charmander represents his sex drive ( not his sexuality like brock ) at first it's a cute easy to control thing, but eventually becomes a raging inferno of disobedience. acquiring his team means getting new issues, but as he trains them, he works said issues out.

The wild pokemon are his rationalizations of the functioning of the world. it's the "a wizard did it" syndrome. If he doesn't know how it works, his mind says pokemon.

Other trainers are more direct forms of his issues, ones that he must either come to terms with or outright defeat.

And gym leaders are more primary aspects of his personality with each pokemon being stronger than the last, to display a level of skill he could be capable of if only he gave into it. in effect he is doing battle with a part of him that he would rather not have in control.

His rivals and the Elite four are ultimately the strongest part of this cycle. Having pokemon that are essentially godlike, they represent both what can be attained and what is unattainable.

Mewtwo was a new form of treatment, done with electric impulses and a machine to knock Ash out of it, taking down every last one of his mental guards (the original pokemon in the movie).

In Ash's mind, Mewtwo and his clones were the treatment for the mental safe guards that were protecting Ash and keeping him comatose; the pokemon of his world. The clones were counters to Ash's mental safeties, and so each appeared to Ash as the exact copy of his defense, intended to take it down by Force. The clones didn't play by the rules of Ash's world, they didn't use any special pokemon attacks or moves -they just beat down their counterpart by brute strength.

The treatment was working, but there were side effects. The electric jolts were beginning to effect Ash's nervous system, and if the treatment continued, he would be paralyzed. His mind realized this and manifested it to Ash by petrifying him in his dream. Were it not for the end of the treatment by Ash's mother (knowing her son would never want to live in a world he couldnt explore) Ash would have remained as stone in his dream.

After this, Ash needed to recover from the damage of the electric therapy. Obviously it was greatly dangerous to him, and in order to reduce the danger Ash's conciousness felt from it, Ash's subconcious began downplaying the effects of electricity in Ash's world, which is why Pikachus electric attacks -once noted for their strength by team rocket- no longer have any effect on Ash, other than comic relief.

Koffing and Ekans were symbolic of team rocket's willingness to change. hence the evolutions. once his mind beat that roadblock down and allowed them to change once, it gives him the chance to truly change.

Pupitar is a rationalization. a pokemon that a rival caught before he met him. Even Ash would become suspicious if everyone he met had no carry-over from pervious places he had been to.

The professors, like the Joy's and Jenny's represent stability, and ash's ideals. This is why gary became a professor.

Misty is an image that ash had of a girl,(this is why she plays so prevalently in the series but is ultimately unattainable before the coma. Likely the one that helped get him to a hospital.

I have a theory in line with this: Since Misty was his initial love interest (if only subconsciously), he needed her to reach a level of womanhood. He felt that people could only have relationships when they've matured. But in practice, it turned out he couldn't cope with it and just wanted the normal, pushy, arrogant Misty he knew, and wouldn't let her keep Togepi anymore. This was also traumatizing to him, being attached to it. Since then, the thought of anyone around him maturing to adulthood has been blocked, and anyone who shows signs of it will quickly end up leaving for another, more naive fill-in.

On the prevalance of ash's japanese heritage and why he lost his beloved hat for a new one.

The same reason he discarded his original hat. He wanted to travel and broaden his horizons, every time he reinvented himself to do so, he lost touch with his original self. If he ever does escape the coma he'll likely have achieved a sort of zen state. Considering the amount of personal issues he deals with inside his head, it's entirely likely that he was the next Poke-Buddah, and that the lightning strike and subsequent coma are a way for him to realize his true self, and destiny.

On tracy and the photograhper friend.

Or things he'd wanted to do when he grew up, before he lost all touch with the concept of aging, having no need for it anymore. He kept those things with him, but not with himself - that would mean learning those skills which would mean growing up. It's sort of like when you want to be a astronaut or a doctor as a kid, Ash wanted to do arts.

on ash's Team

Bulbasaur was ash's unwillingness to change, this is reflected in it's unwillingness to evolve and how it almost decided to stay behind unless he battled it.

Squirtle was his willingness to follow the lead of others, as evidenced by the gang it ran with.

Butterfree was his crushing loneliness, which he dealt with when he released it to join a flock.

His bird types are his recklessness, always willing to sacrifice something at a moment's notice for the win.

If you noticed the early episodes of pokemon were of amazing quality. I believe that when ash was struck by lightning he was put into a coma. The rest of the series is just the results of his subconscious mind fulfilling his desires, as well as attempting to escape them. should ash realize he's in a coma, he would wake up, but suffer brain damage. So he has to take down all his mental barriers one by one until he can come to grips with who he is and escape his coma.

He justifies anything he can't explain with pokemon, and real animals fall into the background because he has no real interest in them.

His travelling partners are actually aspects of himself he can enjoy, but doesn't like to associate with himself. Team rocket are his qualities that he Deems "negative", but is coming to terms with. However the team rocket organization has his abusive father sitting atop it. Jesse and James want to appease the father figure. Meowth especially wants to appease him because he remembers the good times with Giovanni.

Jesse is is Ash's vanity and gullibility, she will trick ash's submissive homosexuality into doing her bidding so she can Please father.

Now James is Ash's Latent homosexuality, hence why he is constantly punished by pokemon and attacked by random attractive girls. I believe the split between ash's parents was caused by this part of ash, maybe an incident at school, bringing shame on the family and forcing them to move to the hick town of pallet. Ash's motivations for his journey were to escape mounting pressure at home.

Pikachu is Ash's Humanity, this is why team rocket is always trying to capture it and bring it to Giovanni. They want father's love. This is why Ash sometimes Joins Team rocket to search for the lost pikachu. However what is unrealized is that Team Rocket also holds a part of Ash's Humanity in meowth. This is apparent in the fact that meowth is the only pokemon capable of speech.

Brock isn't just Ash's latent sexuality, he's also his fatherly instincts, neither of which Ash can come to terms with. Brock leaves his siblings to join the journey because Ash can't cope with having that much responsibility, much as his foray with a real relationship ends on mysterious terms. Ash just cannot handle commitment at his mental level.
It could be a possible view on Ash views his own mother. The massive amount of children could be a suppressed varient of her (Ash's mother in a different guise) being a whore, and her messing up the gym and Brock's life is rage Ash has at his own mother for not trying harder to keep Giovanni around or even for keeping him alive as he's in a coma.

By having this as the mother of one of his different sides instead of "his" own mother, this leaves him in a place where Delia can be sainted. Delia is not a whore, at least not in his mind; Delia is a good woman, who's happy to stay at home and remind him to take care of his wash.

Ash's Rivals are possible futures he envisions for himself (note that they are all older than him). This originated with Gary Oak, Someone ash knew from real life, and built up into a sort of god within his mind. Gary, however progressed and changed to suit Ash's vision of himself and ultimate desire, eventually settling down into a professor after beating the Elite Four.

With Gary in retirement his mind needed a new rival for him Thus the births of Richie ( the Good aspect of his rivalry) and Paul ( as the darker aspect, a cut-throat ash, willing to do anything to escape the coma world).

That episode about Gloom must have related to "Girls only clubs" in Ash's younger days, and his acceptance of perfume at the end and cross dressing were ways he tried to justify his sexuality or wanting to fit in with the girls.

Tracey, The Breeder was a possible future for ash that he discarded. It was one that he sent off to work with the Professor (the professors being ash's ultimate ideal of a father figure) when he disrupted the dynamic ash had with his other possibles. Ash's mind is fighting the coma and since Ash viewed this one as a companion he was quickly replaced with a more threatening Rival.

Back to summarizing.

The Legendaries Are ash's mind telling him that he has the power to do great things, and thus escape his happy- go lucky reality.
The Jenny's and Joys are symbols of comfort and normality, hence why they're everywhere.
Brock is a Projection of his sexuality, and is constantly shot down because ash can never KNOW sex.
Misty is ash's first attempt at a girl he could love, however, being a girl from the real world, that all he knew of her was her anger, she ended up very angry. Constantly berating his sexuality, but eventually mellowing out until she had faded into the background.