65 million years ago a mysterious legend known as velocidon was roaming the land but before it couild lock onto its last mission it died and was turned into a fossil.
Okay, first off, one line does not a chapter make. Unless you're Steven King. And Steven King supposedly did it on
speed. (As in, the kind you have to buy and ingest.) Or maybe that was another novel.
Anyway, you're missing a couple of commas. The first goes after "ago," as this is an introduction clause that's more than four words long. So, you'll need it to separate that part of the sentence from the rest.
The second comma goes after "land" because this is a compound sentence, or a sentence in which a couple of clauses that
could be full sentences are put together by a conjunction (and, but, for, nor, or, yet, so). To see what I mean, cover up the last part of the sentence (the part after "but") and read the first part aloud. See how it's a sentence on its own? Now, cover up the first part (the part before "but") and read the
last part aloud. Another sentence. So, what you need to do to show that they're two independent clauses (i.e. clauses that could be their own sentences), you need a comma before the conjunction (in this case, "but").
Additionally, you misspelled "could."
As for the story... there really isn't one. As I said before, one line does not a chapter make unless you're Steven King on drugs. And even then, it's usually for extreme emphasis of a really important part between two longer chapters. Right now, as a reader, I'm not really caught by your story. I have nothing to go on to want to continue. Just a dangling line.
Additionally, I'm not sure what you mean by "lock on to his last mission." O_o Do you mean before he could
go on his last mission? Before he could
receive orders for his last mission? Who would employ a fossil Pokemon, anyway? And even then, how did he turn into a fossil? As in, how did he die? Additionally, what was his last mission? All of those are ideas on where to take your chapter from there, so you should really sit down and think about where you want to go, rather than post just what you have right then.
Speaking of which...
uh writers block alert
If you're typing this in the reply box of PC, don't. You should really try writing on a word processor such as Microsoft Word or Works or an equivalent. The reason why is because that way, you can save your work without having to post an incomplete chapter.
That way, we only read a complete installment, rather than something that you feel isn't your best work.
Additionally, saving on a word processor gives you the following advantages:
1. More time. You're not as rushed to get a chapter up because no one can see it. Hence, no one really expects you to get a new chapter up right away, and you can get away with spending a bit more time writing and proofreading.
2. The ability to spell check. That way, you can catch misspellings that you wouldn't catch in the new thread box.
3. Search feature, for finding points in longer works that you want to change.
4. The ability to send a document to a beta without posting it online.
And numerous other neat features that are there for writers. (Don't use Microsoft Word's grammar checker, though. It's practically useless.) So, don't write your story on PC. Do it on a word processor and
then copy and paste it to PC.
Overall, it's hard to judge this work because it's only one line long. (I only glanced over the prologue because I felt a bit confused over who was speaking and how fossils -- normally petrified dead organisms -- can attack. Maybe fossil
Pokemon, but not fossils themselves.) The concept has potential, but otherwise, I'll need to see more content to be able to properly judge.