Jeremiah is flat-out nasty; all the bad things that Peter Pan's Lost Boys could have turned into, wrapped up in one furry little ball of spite. It's not that he's actively evil, it's just that he's utterly amoral; devoted almost exclusively to his own pleasure. His only noble impulses are directed toward his twin and, with Robin's growing devotion to Lady Sascha, even that tie is melting away. Jeremiah's anger comes more from the idea that Robin is paying attention to someone else rather than Sascha specifically, but she has become the focus of his malice. It is because of this that he has been receiving overtures from Lord Denis.
On his brighter days, Jeremiah is a joy to be around, devilishly funny, and charming. Most of the time, though, the laughter at his jokes comes as much from the relief of those who were not his targets as th humor of the jests themselves.
In mortal seeming, Jeremiah is utterly indistinguishable from his twin. To Kithain eyes, though, there are subtle differences. Jeremiah is more muscular and fairer as well. Robin may be the image of a harmless squirrel, but Jeremiah has the predatory visage of the weasel. He disdains clothes entirely and is the epitome of the "wild child" image; all feral smile and quick fingers. Where Robin's eyes are green, Jeremiah's are a poisonous yellow.
Jeremiah's chimerical companions, which he shares in some ways with his twin, are little tarsier-like creatures called "Smoofs" that clamber through the trees wherever he goes. They have soft, round eyes and brown fur and there are no real claws on their pink paws. They chitter and laugh incessantly, often speaking with human voices, and Jeremiah has discovered that they can serve much like a remote microphone. What one hears, the others hear as well, and a Smoof in a tree over Lady Sascha can really what it hears to a Smoof in Jeremiah's hand. Robin, while aware of this ability, hasn't put two and two together concerning what can be done with these powers. He prefers to play with them, and can spend endless hours grooming them.
Jeremiah is cruel, vicious, and sarcastic, and that's on his good days. The world is nothing so much as raw material for his jokes and he intends to make the difference between the raw and the cooked very plain. He pushes things as far as he can with insults, practical jokes, and brutal put-downs, then retreats behind the mask of childish innocence when it looks like his actions are about to catch up with him.
Lady Sascha has nothing but his contempt. For that matter, just about everyone has nothing but that contempt. Sascha is on of the hated sidhe and the other residents of the freehold are intruders on what was his brother's and his. Robin?, well he's the worst of all because he has sold out to the uptight, prissy dictator. In his own twisted way, he shows his love for his twin by trying to set him back on the "right" path. Of course, this noble effort requires attempting to shatter his devotion to that girl and Robin isn't buying any of it. Still, Robin is his brother and, as such, deserves on more chance... maybe.