webshooter, I'll apologize in advance since I'm usually terrible at explaining things, and this is going to be especially complicated.
Ok, imagine the control stick as a clock with you facing 9 o'clock. Now imagine a line splitting it directly in half vertically (so a line from 6 to 12).
If you are facing 9, and you activate gyro by moving the control stick to 5 o'clock, you will pivot.
If you are facing 9, and you activate gyro by moving the control stick to 7 o'clock, then QUICKLY slamming the control stick to 3 o'clock you will b-reverse (what you called a wavebounce, but they're actually different things).
*So its actually all based on which side of 6 o'clock you start on.
A wavebounce is actually just a pivot and a b-reverse performed in succession, and I'll include a brief description:
If, once again, you were facing 9 o'clock, and you activate gyro by moving to 5 o'clock (causing a pivot) then QUICKLY slam the stick back to 9 o'clock (causing a b-reverse). The whole thing is a wavebounce.
*You may notice whenever you wavebounce you will be facing the same direction as when you started, as opposed to a b-reverse in which you will face the opposite.
So basically, a b-reverse is the mechanism of using a b-move to switch your momentum, while a wavebounce is a double reverse.
*note: whenever you want to perform a b-reverse: Perform your B move of choice in one direction, then quickly slam the stick in the opposite direction you are facing. Works for most B moves, including ROBs Up-B, gyro, and laser. Works for his side B too but is not as drastic.
hope this helped man, welcome to the boards.