SOLVED. Adult Fantasy series. World has been split into 4 based on the elements & each world is supposed to interact with another has a magic system based on runes drawn by the characters & there are 2 classes of magic that are very... Read 2000-2004. [s]

[Kio]

... obviously a yin yang motif especially with the mage's hair depending on the magic they cast being either dark with light tips or light with dark tips. the most details I remember have to do with the wind based world where everyone is on floating islands at various elevations. in this world water is very scarce to the point that they use it as a currency. There is a guild of thieves and assassins that use a ranking system based an arm holding a sword (The lowest tier starts at the scabbard, then it goes to the tip and so on with the guild master being the whole arm). At the bottom of this world is a large machine that facilitates spouting up what limited water exists in the world up to the other islands. It is later revealed that it was supposed to be connected to the water world (A world that is just a giant ocean with I believe only a single large predator in it), but the connection wasn't working properly which is the reason for the scare water resources in the Wind world.

It's so annoying that I can recall all of these details, but can't recall the title or any of the character's names (Apart from one assassin/thief who just goes by his title of "The Hand"). Makes searching for it on google very difficult. XD

[Robert]

The Death Gate Cycle, by Margaret Weis and Tracy Hickman starting with Dragon Wing?

"Hugh the Hand agrees to assassinate the king's son but is unprepared for the magical being who is his victim's guardian or for the difficulty that awaits him in the realm of the dwarves."

[David]

100% The Death Gate Cycle (one of my personal favorites), just the header information is enough to pinpoint it.

Several other important characters: Haplo which uses one of the two kind of magic and Alfred.

[Kio]

Yes, it is indeed the Death Gate Cycle series. Thanks for the help, Robert and David!