In terms of the wings, the closest I've ever come is some classic Spiderman armpit webs (which apparantly I've never made a single render of), and that's a far ways off.  Still, I figured out how to make those by looking at rawarts creature wings, specifically his underarm models, and the way those were rigged.  His underarm wings are really just fairly simple geometry that's been textured and transmapped.  If I were going to try to make underarm batwings, I think I could either take a very similar approach or model something more detailed and still rig them in a similar way.  If I was feeling less ambitious I suppose I could just make a texture and use his underarm figure.  Or, if I really wanted to just get going with it, looking at the products page for the creature wings, it appears they have an addon pack that has underarm batwings, so if I wasn't feeling diy at all, I might just buy that.

As an alternative approach, you might be able to do something dynamic.  This is pure speculation, but I remember a swidhelm dragon that had dynamic membranes on it's wings, and I've seen various dynamic dresses with wing like features.

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