Speak with Gymer to begin.
I will stop at nothing to see them all driven from this world. We will work together to destroy the Scourge that threaten Zul'Drak.
We will kill them all: Navarius, Algar and Thrym!
When you are ready, let me know and we will begin our destructive journey.
And I was there to see it all happen...
Gymer has the following abilities you can use while riding him:
Gymer's Smash: Gymer smashes his fist into the ground, causing 5363 to 7637 damage to all enemies in a 12 yard radius.(30 energy, 10 yd range, instant, 1 sec cooldown).
Gymer's Roar: Gymer lets lose a deafening roar, knocking back all enemies in front of him and causing roughly 400-1600 damage. (50 Energy, instant, 5 sec cooldown).
Gymer's Grab: Gymer will grab a Vargul that he can then use as a living weapon! Also used to grab Storm Clouds (see below). (30 yd range, instant, 10 sec cooldown).
Gymer's Throw: Throws the Vargul that Gymer is holding in his hand. Will explode on impact! (Unlimited range, instant).
Once you mount Gymer you will be phased, and only see the set mobs (trash mobs and the boss mobs) and other players doing the quest on their Gymer. You should zoom out your camera as far as the video settings will allow. It has been reported that Gymer has an auto attack, but will not use it after his action bar attacks; you must activate it by using the 't' key or right-clicking your target. It may be a similar experience as the Oracle quest  or the Frenzyheart Tribe quest  .
While on Gymer, you will see small purple sparkly clouds near the ground. These are Storm Clouds. Picking them up with Gymer's Grab ability (button 3) will heal him over time for about 50% of his full health. This is crucial for surviving the later portions of this quest. Remember, you cannot pick up a Storm Cloud if you have a Vargul in your hand. You'll need to throw the Vargul first.
Most players prefer to kill Algar first. He is to the northeast, near [30, 45], around one corner of the Voltarus complex. He is fairly straightforward to kill. Make your way south to Navarius. You will likely get your 100 trash Scourge from defending yourself. The trash will instantly respawn, so try to make your way to clear spots with no mobs if you need a breather and grab a Storm Cloud on the way.
Navarius is the human-sized guy inside the purple bubble, around [32, 64], just north of the main steps up to the next region of Zul'Drak. Once you kill Navarius (remember to be aware of when he uses Soul Deflection), Thrym will spawn on the wall above Navarius' spot, then jump down to attack you. Try to save at least one nearby Storm Cloud to grab after he engages you and not before. Be careful: if you run too far in search of a Cloud, you can de-aggro him, and he will despawn. You will have to kill Navarius to spawn him again.
After Thrym is dead you can ride back to Crusader Forward Camp for turn in, or ride around and see the sights. Players have reportedly been able to "duel" other players, through the use of Gymer's knock back ability.