I've noticed the materials for the Illusion Tomes have been climbing in both demand and price, so i checked out the the prices on Essence of Water, turns out they go for anywhere between 100g - 300g each!
I then went and checked how many i could get per hour, on my first try i got 66!! of these badboys in one hour!
Location : Swamp Of Sorrows - far west near the pool ( cords: 19/59 )
Target: Purespring elemental
Spawn time : Seems to be on a fixed spawn, almost instant
Any class can do this, as you can see in the video down below, you can use a class with mobility and pulling power to gather them up and AOE them down!
Hopefully you guys have luck both farming and selling these! Feel free to come with advice and tips about similar/better spots