Let me give you one example from the first post.
"You find yourself in a new world unknown to you..."
This sentence fragment contains an example of a grammatical and compositional error called redundancy. A "new" world is always "unknown." Otherwise, it wouldn't be "new!" Redundancy errors set off a native speaker's grammar ear, creating a similar sensation to hearing the sound of nails on a chalkboard.
The following sentence fragment:
"Purgatory, a world full of dangers and threats, you have to solve the mystery of this world and find friends to survive and go further into the unknown."
These are two independent clauses. They must be punctuated as separate sentences; we can also make use of a semicolon to separate two independent clauses--rarely, we may use a dash to indicate a longer pause before introducing a new independent clause. So the correct version would be: "Purgatory is a world full of dangers. (Saying dangers and threats is another redundancy.) As the main character, your task is to solve the mystery of this world. And if you want to venture further into the unknown, you will need to find friends to survive."
There's a great book called The Elements of Style, which better describes what I'm trying to explain here.