Does this sound good?

[Palamon]

Okay I'm planning on making a fan fiction called Pokemon pearl destiny.
It's about a boy named Fecback(I'm a girl in real life) (I made that name up cause I decided I wanted to be a boy in my pearl and and be a girl in my diamond)
It's based on Pokemon pearl and how team galactic wants to control the world however instead of just palkia there is also dialga arceus shaymin giritina mesprit uxie azelf cresselia & others. His rival jun is trying to beat him to everything.
I will make him beat cynthia I'm sure then it will end a long time from now...
Unless you want me to add.... The sinnoh battle frontier to make it Pearl Platinum fic!
Should I or should I not?
Is this a good idea?

[Giratina]

Warning! There is a strong opinion contained in this post that may not be suitable for anyone who cannot handle honest thoughts from the universe at large. Be warned.

So, in other words, it's exactly like all of the other stories about fledgling Trainers with a name that isn't even real who go on another Average Ordinary Everyday Life-Changing, World-Saving Journey, except this time Team Galactic want to take control of a ridiculous amount of Legendaries that will probably do nothing to further their goals and just make it that much more obvious that they are, indeed, villains?

Uhh... let's start from the top. Notes in bold...

Okay I'm planning on making a fan fiction called Pokemon pearl destiny.
It's about a boy named Fecback (I'm a girl in real life (So?)) (I made that name up (Stop here. I would like to take this time to redirect you to Behind the Name, a lovely website which has an extensive database of first names. It's better than making one up that sounds like it belongs to a werewolf in Harry Potter.)

cause I decided I wanted to be a boy in my pearl and and be a girl in my diamond (So what? Why does this help us at all?))

It's based on Pokemon pearl (Clearly, seeing as it's called Pearl Destiny - which is an extremely overused name, by the way. Maybe try thinking up something better?)

and how team galactic wants to control the world (I thought they wanted to blow it up? You have your evil teams messed up... Team Rocket wants to control the world.)

however instead of just palkia there is also dialga arceus shaymin giritina mesprit uxie azelf cresselia & others. (I've never heard of a Dialgaarceusshaymingiritinamesprituxieazelfcressel iaandothers... what is that Pokemon again?)

His rival jun is trying to beat him to everything. (No surprises there.)

I will make him beat cynthia (You'll make him beat cynthia? I didn't see that coming at all! And goodness, how cruel of you to make your character do something...)

I'm sure then it will end a long time from now... (No, it won't. You'll give up quite early in, I bet.)

Unless you want me to add.... The sinnoh battle frontier to make it Pearl Platinum fic! (Uh... what?)

Should I or should I not?
Is this a good idea?

There was nothing in that paragraph that made me want to read your fic more than just start over my copy of Diamond and follow the exact same plot. I strongly suggest you scrap this 'idea' (it isn't even your idea) and ty to think of something more original and interesting.

[Shiny Loser]

Hahaha I bet she probably listened to the warning xD

That being said, you should scrap this if you haven't already. Originality is key, and from what I've seen based on the description, you could work on your writing skills before you try and pull off something like a fanfic. No offense intended, mere opinion.

[Professor Geoffrey]

My honest and sheer opinion is that it is not original. Make it with your own twist. What makes a twist in the story that makes it entirely different from D/P/Pt? Are there any original characters in your story besides Fecback?

For example, I might make my own Pokemon fanfiction similar to the games. But what's the difference? The main character has powers that seem to be unfathomable. The main goal is not to defeat the champion, but rather to defeat "an ancient evil that resides in the Dimension of the Unown," and has things I added to it that makes it seem different from the games. What I'm doing is making the Pokemon league like doing contests in the games; it's not needed to finish the story, but it is required to complete it. Not saying that you need to do it. All you need to do is add a whole bunch of original stuff that you made. Make a few extra towns. Add a few extra characters. Visit unexplored lands. Add extra islands that haven't been inhabited. Even create your own Pokemon if you have to.

[Kayden Javlaíakín]

I pretty much agree with everyone above. This sort of premise is nothing novel in the fanfiction universe, and it would be difficult to pull it off well enough that it doesn't feel like the same, formulaic foundation that we've seen multiple times before. It would probably be much more beneficial to try and find your own footing in writing and develop your own, original plot and form your fiction around that.

Not to sound mean, but this sort of idea's been done to death, and I'm - as many others are, I'm sure - tired of reading the same thing over and over and over again. Also, it seems to be a trend among new writers to insert a crapload of legendaries into their stories for no apparent reason other than to act as... "plot lambs", I should say; that is, characters whose existence in the story is pretty much unwarranted except to serve as beings in dire need of rescuing. These are fine, if you can pull them off convincingly. Of course, you've only posted a brief summary of your fiction, but it definitely sounds like it's going to take a trip down that path.

I also do hope that, as Shiny Loser already mentioned, your summary isn't exemplary of your ability. :s