That is a very nice and creepy pic. Actually, I would have been happy if they had designed Quicklings like that. The only problem I see with that design is that it is too similar to a pixie. Casual gamers are going to have a hard time distinguishing between one type of tiny winged elf from another.
This got my wheels turning, so I quickly sketched out some pics of what a quickling would look like in motion. The awkward body lends itself towards a creature that is meant to be in constant motion, one that
needs to run. I like the idea of a quickling feeling uncomfortable when walking or standing. Those big claws would also be highly useful for sudden turns at high speeds. It could dig into the ground for sharp turns or stop suddenly by using its claws.
I also think the strange leg anatomy makes sense. The quickling would need to sleep “standing up” by sitting on its own legs. That means, even while sleeping, it would be ready to go at a moments notice. Something like this: