Thanks a bunch OddYuko! Sorry about the double post. It's just one of my blunders in trying to get used to the way this website works. But I will make it up by posting up something I'm working on right now later. I was thinking of posting this one again on a different thread, just so people can see it right away.
As for the creature my steef is fighting, it's actually an ancestor of the wolvarks. I figured it would make sense, since we hear steefs evolved as guardians of the Mongo river.
Anyway, in this version of Oddworld history, the wolvarks originally were semi-aquatic creatures that came from the northermost regions of the Mongo River. They were fine as long as they stayed in their region, but once the industrial species discovered their love of Grubb flesh, they sent them to the area of the Mongo river that we know and love as an early attempt of Grubb "control." Here, these early wolvarks acted as invasive species, almost wiping out the Grubb population along the Mongo river. The Steefs managed to hold the Wolvarks back and eventually drive them away, and the industrial species performed many acts of "positive eugenics" on the remaining wolvarks so that they evolved into a class of blue-collared grunts. Kind of like what we've done to pigs and dogs.