A development of someone elses idea: The islands are being raised by a kraken or something similar. The kraken waits decades or centuries, allowing the humans and other races to colonise the islands, and them sinks them, letting the pitiful creatures drown and feast en masse on their corpses... (or, gathering them as part of a vast necromantic construct, designed to elevate it to godhood / destroy the primordial enemies of the kraken race / complete it's brand new modern art installation).
Another idea: If they drift, perhap goblins / lizardfolk use the islands as sloooooow but mobile siege towers, ramming them into other islands (thanks to a new PrC, the IslandDriver!) and storming them. Or is this too silly?
Another idea: What if the Crossing from the Green to te Grey is caused by an imbalance in a cosmic principle... say, Law vs Chaos, or Energy vs Entropy. To keep the universe from shattering, the 'weights' (islands) must be moved from one domain to another. It is a constant, dynamic process, maintained by (whatever outsider suits your purposes... Modrons!)
Church of Saint Illiax (the Vigilant) LE: Act as a mercenary force and militant order, a counterpoint to the Church of St Alain. They protect the weak and defenceless, with the price that they be allowed to install governors and tax collectors of their own devising in protected lands.. They may be at war with the Chevaliers.
Church of Saint Kellera (the Corrupters / the Decadent) NE: Work to destabilise other faiths, transforming holy men into selfish gluttons and deviants.
Church of Saint Bronehgild (the Savagers) CE: Follow a pseudo-druidic path of might makes right, hairy makes scary, believing that Auros never meant for Men to rise above Beasts in behaviour.
Myth ideas:
Finding of the Book of the Three-Fold Heresy: This myth tells the tale of how a hermit monk, living over a millenia ago left Mainland to dwell in isolation on the island (at the time, there was only one). There, he discovered an ancient, crumbling shrine that contained symbols of Auros the Mighty but predated any known manifestation of the faith.
The shrine contained a tome, which the hermit discovered detailed previously lost aspects of the faith; for Auros had seeded factions that believed both in weal and woe, in help and harm, but the good faiths had driven their evil kin to extinction ages ago. The hermit resolved that he would refound the dark orders, because that was Auros' wish (or so he thought... was the book in fact a theological trap laid by the Gods or Demons of Naughtiness? dun dun DUN!)
Perhaps it was finding a copy of this manuscript in one of their scriptoriums that drove the first Alexandrites to corruption and evil.
The Returned: Not all who were taken to the Grey Lands stay there. Tales say that the island of Rydimios fell into the Grey Maelstrom eight hundred years ago, one of the first places in the archipeligo to Cross. Three hundred years ago, however... it came back. The people and the land were changed by their sojourn in the shadow. All colour seemed bleached away from the trees and grass, the animals were still and feeble, and the inhabitants were no longer human. They had become... (elves? faefolk? changlings? dopplegangers? up to you).
And, finally...
Skartha (lesser kraken / krakenspawn)
Medium Magical Beast
HD: 2d10+4 (15 hp); Speed: Swim 20 ft; Armor Class: 14 (+4 natural), touch 10, flat-footed 14;Base Attack/Grapple: +2/+5; Attack: Tentacle +5 melee (d6+3); Full Attack: 2 tentacles +5 melee (d6+3) and 6 arms +0 melee (1d3+1) and bite +0 melee (d8+3);
Space/Reach: 5 ft./0 ft. (10 ft. with tentacle); Special Attacks: Improved grab, constrict d6+3 or 1d3+1; Special Qualities: Darkvision 60 ft., ink cloud, jet, low-light vision; Saves: Fort +5, Ref +2, Will +3; Abilities: Str 16, Dex 10, Con 14, Int 12, Wis 13, Cha 12; Skills: Intimidate +6, Listen +6, Spot +6, Swim +11; Feats: Iron Will.
Improved Grab (Ex): To use this ability, the skatha must hit with an arm or tentacle attack. It can then attempt to start a grapple as a free action without provoking an attack of opportunity. If it wins the grapple check, it establishes a hold and can constrict.
Constrict (Ex): A skatha deals automatic arm or tentacle damage with a successful grapple check.
Jet (Ex): A skatha can jet backward once per round as a full-round action, at a speed of 60 feet. It must move in a straight line, but does not provoke attacks of opportunity while jetting.
Ink Cloud (Ex): A skatha can emit a cloud of jet-black ink in an 10-foot spread once per minute as a free action. The cloud provides total concealment, which the kraken normally uses to escape a fight that is going badly. Creatures within the cloud are considered to be in darkness.
Environment: Temperate aquatic
Organization: Solitary or pod (3-12)
Challenge Rating: 2
Treasure: Standard
Alignment: Usually neutral evil
Advancement: 4–6 HD (Medium); 7–12 HD (Large) or by class (often fighters or sorcerors).
