The Rogue Titan, also know as the Eren Attack Titan, is a playable titan that you can use in single-player mode. If you select EREN_TITAN in single-player mode, you can play as the Rogue Titan for as long as you want. But if you select EREN, you can only use it for 15 seconds by right-clicking.
The Rogue Titan in-game.
When you play as the Rogue Titan, you can punch by left-clicking and kick by right-clicking. And as always, WASD to move. You can also press N to roar (headphone users, beware.)
The Rogue Titan roaring.