@R_R_X, once again you're establishing LIM as a real contender in the industry.
I love your teeth on this sculpt. Honestly, are you considering releasing this sculpt with a normal paint app as well? I think many folks would double dip, myself included. Maybe a different hat in a limited third run?
Looks to me like you've got the teeth edge to edge as if Arthur is pushing his jaw forward while trying to breathe harder.
Which, if what you're going for (I imagine so), then you're doing it VERY well. You're essential trying to capture what we call anterior guidance for mandibular movement. When the jaw shifts forward, the front teeth naturally separate (in most folks) the back teeth. Arthur is never portrayed with a flawed bite in game, so this is a pretty accurate portrayal of normal eccentric (those which are not up and down) movements of the mouth.
I might suggest you tilt the angle of his gaze so he's looking upwards a little more. It'll emphasize the labored function you're conveying in the overall presentation.
Because you're not having him elevate his upper lip, your exposure of just a bit of his upper central teeth is accurate. In a resting, semi-open mouth position you should only see about 1-2mm max of a person's top front teeth at Arthur's age, so this is accurate. Retraction of the lower lip to allow for his labored breathing and a pushed forward jaw would generate the shape of the mouth you're depicting in the sculpt, exposing the lower teeth.
Regarding the teeth, your finish is outstanding. I'm assuming you're casting in a semi translucent off-white resin and staining with yellows and browns before glossing?
If you wanted me to get really picky, I'd say some of your lower teeth could be altered in size and shape a little but we're really splitting hairs on that, especially at this scale.
I'm sure some folks here are going to hang me for this, but your teeth (and quite frankly a number of other facial attributes) outdo InArt. Edit: to really rustle jimmies, this looks miles better than they reported production Joker sculpt pics from them. They should set your production product as their standard to beat for their first outings.
Tl;Dr love the sculpt that the care you put into the teeth and mouth. Teeth are hard to make at 1:1 scale, so doing this good at 1/6 says a lot. Please don't change your production here, this is very good for what I feel you're trying to convey. Y'all are killing it.