There are four world quests in The Forbidden Reach against Flow, Tremblor, Vortex, & Wildfire.
The stats & quality of the enemy can be reduced from Legendary > Epic > Rare if you defeat two (sometimes three) of the smaller enemies in the small area around the WQ enemy. This weakening will time out, causing them to regain their previous qualities, and you will need to re-battle the smaller enemies to re-weaken the WQ NPC again. It appears that other players can benefit from someone else weakening the enemy, so if you weaken it down to rare it will weaken down to rare for everyone there at the time, too.
Additional Information: Defeating this enemy in its RARE form will also reward an item that teaches a pet by the same name. You will not receive the pet while defeating the Legendary or Epic versions. However, you can receive credit for the WQ while fighting their Legendary and Epic versions.
Xu-Fu can scan this section for the most suitable strategies according to your preferences and show the required pets.
Depending on the amount of fights in the section, this can take up to a minute to process.