I understand the emotional effect you were trying to give with this, but really, all the grammar mistakes, lack of description, altered font, and other errors it's ridden with completely ruined it for me.
For starters (this is one of the first things I noticed)... is there any particular reason
why they had to be
legendary Pokemon...? Right off the bat when you say it's Mew and Shaymin we're talking about, the believability of your whole fic starts to fade. Why? Legendary Pokemon are divine beings. They're the Pokemon equivalent of
gods. Would two gods, in a realistic setting, be prancing about through the forest? No. Canonically, Mew should be roaming the world freely. Shaymin should be in the Flower Paradise, watching over "her" home. There is no logical explanation you can give for why Mew and Shaymin, of all Pokemon, would be "bestest buddies". In fact, you would have given the same sorrow-effect you were going for if you'd just used two non-legendary Pokemon. That would have made it a lot more believable, and I for one would have been able to take it a lot more seriously.
My name is Mew. I'm pink, have stubby arms, and blue eyes.
Shaymin is green and white with a flower in her hair.
Something tells me you've been told to "describe the Pokemon in your fic". I don't think you took it the right way. That doesn't mean "give one sentence that tells all about it and keep writing". That makes it seem like a wikipedia entry, or a description in a Pokemon-handbook. Instead of giving the whole appearance at once, make it more apparent as you write. For instance, you could include a sentence like "I floated through the air, my long tail trailing behind me." Or, "I reached out with my paw and touched Shaymin's grassy back."
Shaymin can change form from land to sky at will.
This does not make any sense. Okay, so it does to any Pokemon fan who's been on Serebii.net in the past month or so, but that's beside the point. In the same way you must describe Pokemon, you can't write fanfiction as if you expect your readers to know all about your subject. That said, someone who doesn't know about Pokemon would be thinking, "Wait. So Shaymin can turn into land? And then it turns into the sky...?" You need to elaborate on things like this (and probably should do so later when it's important, like when Shaymin is actually changing her Forme).
The reason we were walking in the woods was to collect herbs.
Why do they need to collect herbs? And what woods? What is this forest like? We can't place ourselves in the situation at all unless you describe the setting.
That night was supposed to be peaceful but, I kept thinking about my life. Our parents were killed when we were young. When I met Shaymin we developed our own power. When people from another land discovered this power they sent people to kill us. I discovered this plan me and Shaymin used our powers to drive them off. A year later a fire destroyed the village and me and Shaymin fled to the forest. This is a new home that we have adapted to. As long as Shaymin stays my friend I'm happy.
1. According to cannon, legendary Pokemon cannot have parents. And, even if they did, it would have been a
long time ago (as in, thousands of years).
2. What do you mean, "We developed our own power"? What is this "own power"? What does it do? How did they develop it? And why?
3. Like Supah Funk said, why would someone try to
kill you if you had a unique power, but were not causing harm to them? Sure, maybe they'd want to use it for themselves, but you'd have to be alive for them to do that... right? And what of this other land?
Elaborate.
4. What village...? One moment you'r talking about a plan, and teh next a village is being destroyed. It's all very confusing to a reader.
"Mew.", She said to me, "Do you feel like something is going to happen." "No not really." I answered.
Every time a new character speaks, make a new paragraph. Like so...
"Mew.", She said to me, "Do you feel like something is going to happen."
"No not really." I answered.
Also, Shaymin asked Mew a question. This calls for a QUESTION mark. Not a period.
She lost her balance and fell off the cliff. It was a Frosslass that had attacked her.
So after Shaymin fell, Mew automatically knew a Froslass had attacked? Mew did not turn around and see a Froslass approaching, or hear the attacker cry "Froslass!", or anything of the sort? Not to mention, Supha Funk's whole point about Froslass "shooting" Shaymin is also very true. For a moment I was led to believe Froslass had a shotgun, by some unexplained means.
"You… You are going to pay Frosslass. Shadow ball!" I shouted. It evaded the attack.
First, I don't really see why Mew would have to scream the name of the attack. It's not a trainer commanding a Pokemon; it's a Pokemon using Shadow Ball. I think many readers would have guessed it was a Shadow Ball as well if you'd described the attack as something like a purplish orb of dark energy. But, of course, you didn't. In fact, you never even said Mew attacked. Mew just said "Shadow Ball", and Froslass dodged. What it dodged, though, shouldn't exist. It was never shown or specified that Mew began, created, or launched the attack.
Not to mention, why on earth would this random Froslass randomly want to murder a legendary Pokemon? Sure, Froslass is a Ghost Type, and most Ghost Pokemon are known to be cunning, tricky, and sometimes expected to cause harm, but killing Shaymin...? Why? This must be one twisted, insane, murderous Pokemon, and you never gave any reason what it would gain from doing such a mindless thing.
"You try to kill Shaymin, I have had it. Equilizer!" I shouted to Frosslass. It hit, Frosslass fled. I rushed down to Shaymin.
The use of Equilizer is the same as the use of Shadow Ball. And, didn't Froslass try to fight back? I mean, why wouldn't it? The level of danger seems small and insignificant when you find that Shaymin's attacker was a Pokemon who got hit once, ran away, and never fought back. It really makes it look like you were just too lazy to go through with writing out a detailed and complete battle scene.
I won't go into the last paragraph, simply because it would have been great if not for the rest of your errors (and if it had had better grammar...). So, pretty much, you have a story about two
legendary Pokemon who are best friends, were almost killed by people for their "power", found a forest, and were attacked by a Froslass who was brave (or insane) enough to try to kill one of them, but too cowardly and weak to even try to fight back?
It all just seems to lack in many ways. Believability... Grammar... Description... Logic... Try to work on your writing. Practice more. Perhaps get a Beta-Reader? It's not that you have bad ideas; the sorrowful death really was something I could tell you tried to do well at. But you need to work at your writing style.