The game will be available on the existing TERA client for free and is set to feature heroes from the game throughout its history. Here’s the lore,
“After the defeat of Shandra Manaya, strange portals appeared across the world, offering glimpses of other realms where dead heroes lived on, live heroes fell into darkness, and heroes that never were stepped up to save the world.”
To that end, we’ll have to fight through Agaia, a new realm, to battle replicas and more. Players will have to fight through the Tower of Sahara defended by Manahan. Each of these heroes, as expected, will have their own set of skills and abilities. You can customize these heroes as well using both runes in addition to cosmetic items. At this time, the post doesn’t mention how these cosmetics can be obtained. There's no word on a console release either.
You can check out the trailer for TERA Battle Arena below: