You guys realize if you're not using tap jump you can just press Y and B while only using your thumb and not needing to move it at all? You don't need to assign jump to L/R or press jump with your index finger. Have your thumb overtop of both buttons at the same time and press Y with the end of your thumb and B with the other part on the next frame like you'd time a JC grab in Melee. It's also how you can do perfect LHDLs easily with Falco in Melee.
When you Up-B out of shield you should have 1 vulnerable frame at best, which is your jump frame that cancels the shield and allows the up-B. You can do this with either method.
I'm not sure, but I think if you press Y and B and the same time with tap jump off, you'll have 0 frames, since you press at the same exact time (or within 16.667ms (1/60th of a second) of each other).
I record at 480p and 60fps so I can get frame by frame analysis and let you guys know.
One question: With tap jump on, if you hold shield and slow lift the analog stick up and then you have the shield shift upwards, and you press B, will it work?
That might have been too confusing.
Hold L, tilt analog up (SLOWLY) and you should have Marth shield protecting his top half. If you press B, then and there, does the Dolphin Slash come out?
Logic tells me no.
If that's the case, then you have 1 frame of vulnerabilty with tap jump on and 0 frames (if you press Y and B at the same time or within 16.667 ms) of vulnerability with tap jump off.
There is a difference. With a Jump Cancelled Reverse Up-Smash Hit, you can't press X and A at the same time. You need to wait 1 frame after pressing jump. It won't work if you press at the same time. This means it's a slide input (like in some fighters).
But this isn't the case. You can press them AT THE SAME TIME. You don't need to wait one frame to press B. You can press Y and B at the same time.