I did the final battle with the spirit at the dungeon of the forsaken. Where do I go from there?

Astryl's Vale - Ethernia should be available.

Of course, you didn't need to complete the Dungeon to progress to Astryl's Vale so, if you've already progressed Astryl's Vale, you're done for now (until they release the MegaZone).

Thank you for the imfo. How do you beat the elemental beast?

It's been awhile since I completed that area... Are you referring to Vorpa? Or are you referring to the requirement that you defeat 20 Elementals?

If you're referring to Vorpa, I provided a couple of tips and links in this thread.

If you're referring to the requirement to defeat 20 Elementals, they're the annoying blue things that pop-up in addition to Sylesti when you're on the water - you fight them like any other standard exploration battle but just be aware that they can heal themselves somewhat.