Riven can flash during her third Q, and her W to move the AoEs of the damage and CC. Even better when she's ulting and they have larger ranges and AoEs and more damage. She can also E into either W or third Q to move during it to also move the AoE, damage and CC. She can also falsh during the E before the 3rd Q or W to move it twice, once with the E, once with the flash, before the AoE/damage/CC goes off.
Hell, she can also cast her R1 during the E, flash afterwards, and weave R2 into the CC frames after Q3 or W hit. In fact, the full Riven combo has her unloading a W, Q3, R2, 2 autos, and a tiamat proc from flash + E range away (usually from a bush) in under the time that she can CC you from just Q3 + W. I have friends in diamond and masters who have been Riven, Yi, Yasuo and Vayne mains since S3 just for the sheer amount of bullshit those champions can put out, and for their firm belief that if you master those champions you can ignore virtually all attempts by your opponents to either counter play or counter build you. They can be reliably OTPed into high Masters, including with my friends jungling as Riven/Vayne/Yasuo, top laning as them, playing them mid, and even playing Riven and Yasuo support in D1/Masters.