The Dark Shore by A.A. Attanasio is currently free to download from Amazon (US, ES). This is the synopsis of the book:

Here is an epic fantasy from the dawn of Creation, from the first worlds, the Bright Worlds. Among them is Irth. And upon Irth, in a realm of wizards, witch queens, and magic,
destiny casts shadows into the Gulf and onto the Dark Shore, a universe
of blacker magic and deeper mysteries -- the greatest of which is
Earth.
Irth is a world where magic rules -- magic that radiates
from the Abiding Star. The nobility, possessors of most of this mystic
energy, dwell in floating cities that drift above their realms, plotting against each other for domination.
Those
who fail in their attempts to hold or usurp power are cast off the Edge
into the abyss beyond the reach of the Abiding Star. There they fall
into the cold world of the Dark Shore -- onto Earth -- from whence no one has ever returned. Until now.
Hu'dre
Vra, formerly an abject scavenger who found a magical sword but failed
to use it wisely and was cast into the abyss, has returned from the Dark
Shore with an awesome new power: black magic. At the head of an army of cacodemons impervious to Irth's enchantments, Hu'dre Vra the Dark Lord wreaks a terrible vengeance upon the world that exiled him.
But there is resistance to the Dark Lord's rule of terror. The mysterious, inventive thief Ripcat and his crafty partner Dogbrick
form an uneasy and dangerous alliance with the brave young noblewoman
Jyoti and her small band of comrades, among whom is her family's ancient
sorcerer, Caval. Together they all must pit their courage, their wits
and their lives against the brutal minions of the Dark Shore.
A magically charged and enthralling tale of a once-charmed world and the supernatural evil that threatens to destroy it.