Alright... be warned, Omni. If you want good criticism, I'll be constructive, but by the same token you'd better not be judgemental. I'll say what I think needs to be said: You really should have improved your general writing skills before putting this out. It needs major improvement. This does not under any circumstances mean that I think you're a lousy writer, far from it. I simply think that this story needs some major improvement in many basic areas.
1. Grammar:
Your grammar is decent. The story is readable, and I can tell when a new character is speaking. Spelling mistakes appear to be your worst problem- may I suggest getting a beta reader or using a spellcheck? Here are some of the ones I found that stood out most:
Cain was a new pokemon trainer. He was walking through the lush grass of viridian forest. He however didnt like being a pokemon trainer. He prefered studying them instead of battling
No apostrophe.
But all of the sudden Bulbasaur felt an invisable hand grasp him. Then was flung through the trees. Cain was defenseless.
Um... you need to merge the first two sentences. "All of
a sudden", not "
The sudden". "Invisible" was misspelled.
*I mean you will be able to conqure any pokemon or human alike. Your psychic powers will desimate citys and even whole continents. Just by waving your finger.*
"Conquer" and "decimate". Last two sentences need to be merged.
Then quick as lightning a purple blur came from out of nowhere. It was Mewtwo himself yet Cain didnt know what it was.
There needs to be a comma between "himself" and "yet", and didn't is missing its apostrophe. Preferably, both sentences should be dropped in favor of something more like "Suddenly, a purple blur shot from the forest, moving like lightning. Cain was alarmed. He had no idea what it was." You get the idea.
A blur of pink light flying towards the Indigo Plataeo.
"Plateau", not "Plataeo". (Can't say I blame you for that one- it's an easy mistake.)
2. Style:
Your story gets pretty repetitive after Mewtwo and Mew's conversation. Your use of the simile "quick as lightning" twice in such a short period really doesn't do much, and your lack of description is disheartening. I have no idea what Cain or Bulbasaur look like, and about all I know about Mewtwo and Mew is that one is purple, the other is pink. Not exactly the best descriptions ever. Placing thoughts and mind-conversation in asterisks isn't quite as effective as placing them in italics, I've found. It makes you look more professional.
Plot: Not much to go on here... I can pretty much see where this is going, unless you throw in some clever plot twist. Cain falls for Mewtwo's little scheme and ends up getting just as suicidal as the purple cat when it's all over. If you wanted to make it a little less obvious, you could put the conversation between Mewtwo and his "sister" Mew (officially, I've always thought of Mew as being a hermaphrodite, but hey, each to his own) before the introduction of Cain. Perhaps you could make it a prologue? You stated that Mewtwo "hates his existance" in those exact words too many times in a row.
Anyway, the plot here doesn't seem to be suited to a drawn out story. It needs either a quick conclusion or something to draw out the action.
Characters: So far we have a super-depressed Mewtwo, a guy named Cain who apparently doesn't like Pokemon battles yet for some reason still wants ultimate power, and a giggling, know-it-all, supa-wise Mew. I think some serious character development is in order... it pays to know that just because overly peppy characters are stereotypic, it doesn't mean suicidal ones aren't. Mewtwo's reasons for not killing himself are kind of... well, lacking. I'm not really convinced he actually wants to that badly.
Overall: Lacking in many departments. I strongly suggest a rewrite, and some rethinking.