As always, I'm late with the overviews, but here they are:
Iron Leviathanim
The Creatures of Quintatha call these creatures titans, but since this term already has a few meanings in the d20 community, I decided to use a more descriptive name for these creatures.
On average, they are 335 feet long and have a multicolored, shining hide (each Leviathan has a unique hide). They live as solitary predators in the ocean of blood and rust of Quintatha, where the gravity may shift from one mile to the next in unexpected ways. This, and their enormous strength make the Leviathanim dangerous foes for the Barkners, who hunt them for their bones (which provide the raw material for their daggers, and are psionically active), blood and "flesh" (which is actually iron). The only possibility for the Barkners to kill the titans is to rupture their air-bladders, upon which they rise to the surface and begin their day-long death-struggle. The Creatures of Quintatha assault the Leviathan when he surfaces to weaken him enough that he can be transported to Hellmock, the only town of Quintatha - a collection of many ships bound together.
As a (very) quick and (very) dirty conversion, it may be appropriate to take the stats of a cachalot whale, advance him to his maximum HD, and add the axiomatic template (It isn't really accurate, but it is a start).
Rishtyn-Jaffami
(The following overview for Rishtyn-Jaffami is written from the viewpoint of the Perry-Rhodan universe (as usual), but I might later add an overview fitting for the D&D universe)
Rishtyn-Jaffami is the last survivor of a climactic battle that took place above a planet with powerful, 5-dimensional radiation. The Jaffami, who crash-landed on the planet, slowly mutated, with his cells multiplying beyond control, but without dying. He also developed powerful mental abilities, at the price of his mobility. After thousands of years, Rishtyn-Jaffami created Quintatha with all its inhabitants. At that time, he was physically nothing more than a titanic grey blob, so he created a second body within Quintatha - that of a grey titan of a few miles length. In both forms, he could split the pigments of his skin into black and white, creating a strange pattern, which caused people who look at it to see their own faces. In Quintatha, he was also named the Great Grey One.
Later, Rishtyn-Jaffami was enslaved by a humanoid race called the E'Valentans, who came with so many forces that Rishtyn-Jaffami couldn't defeat them all. They forced him to pay tribute in form of Creatures of Quintatha and Quintatha daggers.
In Quintatha, Rishtyn-Jaffami was greatly feared, and on rare occasions even hunted. He lived within a bubble of air within the ocean of Quintatha, isolated from the main ocean with Hellmock. In 160000 years, no Barkner was able to hurt him - except for Shirka, the Avenger, who managed to rupture his air-bladder and cause the slow death of Rishtyn-Jaffami on both worlds.