Gospog said:
JPL,
What about some sort of sea monster to inhabit the Vast Ocean?
Based on a giant squid is the obvious route, I would imagine. It's skin is sticky, like tar, to aid in capturing prey.
But the ink it squirts also acts as a solvent for this "tar". So the best defense if grappled by this behemoth is to startle or frighten it, so that it "squirts" it's ink. A sword in the eye ought to di it! 
That would be the Greater Deepwater Nalthis. The few specimens whose corpses have washed up on the shores of the Vastness are terrifying enough; that scholars have pronounced these monstrosities as 'clearly juvenile' is just one of many reasons no one sailing on the Vastness gets out of easy sight of shore.
The regions of the Grey Empire and other relatively densely populated areas have few of the true nightmare creatures, as such beasts reproduce slowly and need a large area in which to feed; concerted effort by sentients, even those limited to telgir-wood spears and hurled jirathite grenades can remove them from an area. Nonetheless, some things inevitably wander by, or fly over -- there are creatures like giant aerial jellyish large enough to engulf, and digest, a building; there are ponderous, immense, hard-shelled creatures like tortoises which can bear a small fortress on their backs; there are things something like termites but close to a man's size, though still mindless, who build skyscraper like complexes where millions dwell...
None of these, however, are in issue 102.

(What, you think I'd give away the 'Coming soon!' contents?) There you will (probably) find the zorl, the vort, and the bathar, among others.
As Gospog notes, it's a big place. I like large, sprawling, settings. There's room for a LOT.