That strobe light effect is actually what makes me think it's green screen the most, because while it changes the background, which as shown by the OPVs can be a non-manual visual effect, the girls themselves do not change with the lighting AT ALL. Even on the big screenshots posted by ebc there's absolutely no change between when the strobe light is on and when it's off. In reality the change in lighting contrast should change the position of the shadows on their bodies, as well as making the glow on the side of the strobe light go away. It doesn't.
The 2Dness in DS12's OPV only becomes apparent when the camera does a side to side pan, and it's not even that obvious during the first pre-chorus. All of the shots in Bad Girl are stationary or zooms, so as long as they filmed from that angle, which isn't hard as none of the camera angles are positioned to catch the cameras of another, no 2Dness would be apparent.(Similarly, you can tell which shots are CG and which aren't in Visual Dreams by seeing which ones have a side to side pan) Changing the background of the green screen to match the different camera angles isn't hard because you can inherently pan through CG backgrounds. One of the things that actually seems off to me about Bad Girl is that the angle of the girls to the ground and the angle of the pillars to the ground doesn't seem to match on the low-angle wide shots in the garage.
(But that could be just a camera lens thing, so it's not trustworthy evidence for either side)
I'd also like to point out Tokkaiko Junjou. Its dance shot has shadows and everything, but it turns out the harbor setting is a backdrop of some sort because in the full version grey skies have suddenly turned into an orange sunset. Including the lighting on the girls! The lighting change is definitely a visual effect because it's all grey skies in the making of. (Buaaaaaa H!P with better production values!?
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BTW, how do I disable automatic Youtube embed? I wanted to just make them urls.