Alright, so this is two parts. A new zone, and a new class that you unlock by finishing said zone.
You should get an in-game item that explains some things.

Illusory Wood
You'll find this place a couple spaces east of Zigur. Minimum suggested level is 18.
Complete the quest inside and you'll unlock the Trickster class.

Trickster
A psionic rogue.
- Use illusory walls and decoys to distract your enemies.
- A wide variety of debuffs that confuse and distract your foes.
- Turn enemies' confusion into your own power.
- Convince your enemies that they don't see you, even as you stand in plain sight.
- Stabbing things.
The basic idea is that you throw out illusions everywhere to cover you while you stab things to death.

Feel free to offer suggestions/feedback/whatever.