Your time will come. You will face the same evil, and you will defeat it.
In ancient times, the land lay covered in forests, where, from ages long past, dwelt the spirits of the gods.
The first five minutes of How to Train Your Dragon 2!
Not too spoilery, if you have already seen the first and second trailers. The one really new stuff is the dragon races that was also glimpsed in the trailers too. It is an edited down version.
Only the Avatar can master all four elements
and bring balance to the world.