I like the way you describe the gameplay. Seems you want a kind of WarioLand style platformer which is more about platforming and fun than death or puzzles.
I'd like the idea of scaring mudokons away with a disguise, that sounds funny.
The problem with making a Slig story is whether you make him Neutral, or whether he's a rebel and starts killing all the Sligs and freeing all the mudokons.
I think in the Slig game I'm planning, I want the Sligs to be co-operative.
Not sure what the story of my game is yet so I'll have to think about it
I suppose I could always use one of my fanfics as a story.
By the way Xan, that story is quite similar to Oddworld's SligStorm idea, did you ever come across it? It's worth a read to see what it could have been like.