The multishine is a chain of quick, precisely timed shines in between shines canceled by jumps and then shining the frame you leave the ground. This can be very useful for pressuring/breaking shields at an advanced level. More commonly though, its a high-level tech skilled used to show off your mastery of the game. Lets look at the tech frame-by-frame, then put it all together, hopefully giving you insite into the mechanics.
Note: 60 frames = 1 second
*The very first shine acts slightly different because you're grounded as the shine begins.
1st frame - the attack comes out
2nd and 3rd frames - very slight lag, no attack or reflection, the jump button can be pressed during these frames, but it won't take effect until frame 4
frames 4-21 - reflection, can be held longer, but when B is just pressed once, the reflection will end after 18 frames, this is the 18 frame window that you can jump cancel the shine, the sooner the better of course. As soon as you jump you'll enter the jump animation, this is the only time you have to reach the B button.
Now lets suppose you jumped asap:
frames 4-8 - the jump animation lasts 5 frames, you'll be airborne on the 6th frame of your jump
frame 9 - exactly 6 frames into your jump press B+down, this is the most difficult part, you'll have to practice finding the timing to press B exactly 1/12 of a second (5 frames) after pressing Y/X.
frames 10-12 - you're airborne, 2 of the frames you can't do anything, but if you jump on the 3rd frame then you'll doublejump before you hit the ground.
frame 13 - you land on the ground with the reflector active, you have a 15 frame window to jump again, this is 2 frames less than before, because one frame of the reflector was used in the air, and you can't actually input the jump until you've been on the ground for 1 frame.
repeat frames 4-13 as much as you like/can
1)Hold down on the control stick and press B.
2)Press Y within the next 1/4 of a second,
3)press B EXACTLY 1/12 of a second after pressing Y.
4)Press Y within the next 1/4 of a second again, but not too soon or you'll double jump, though that shouldn't be a problem unless you are super fast.
5)Repeat steps 3 and 4 as long as you can.
The important motion is from Y to B
The B to Y motion has a wide window, as long as you don't press Y too soon and double jump you'll be fine, but there is only 1 frame for the B input! Thats only 1/60 of a second.
The timing is like wavedashing
The frame you need to press B is exactly the same frame to press L/R in a wavedash, so if that helps think of it as wavedashing with B.
Jump on site of the first large, hollow, blue hexagon
if you look at the frames there are 3 frames with the white, half filled hexagon, the first frame with the big blue one is when you're able to jump, any sooner and you may double jump, any later and you may miss your window
Fox's double lazer has the same motion Y to B
Fox's short hop double lazer requires a even faster motion from Y to B practice just barely tapping the Y button on your way to the B button, if you can get 2 lazers than you can move fast enough to do the multishine
PCHU's multishine techniques - pretty good video with a couple of techniques he uses, he slides from B to Y though like I tell you not to, but he moves back to B so fast it really just works for him.
The tree in Onett makes it easier because it actually comes back up to you giving you a little bit more room for error on the B
Advancing multishine- just so you can see its possible and what it looks like
Only practical use is of multishining is a relentless shield pressure, to transfer from the normal type of multishining there are 2 more things to learn.
1. Hitlag - There are 4 frames of hitlag for you after you hit, this means you press Y later, but the Y to B motion that I've been stressing is still EXACTLY the same.
2. Advancing multishine - shields tend to get pushed away by an attack, so in order to continue you're attack you need to be moving towards them as they're pushed away. This change is quite simple, hold the control stick down left to move left and down-right to move right. Figure out where the threshold is for Side-B and use your shine by holding just below the threshold
They have 4 frames that they're free between shield stun, less time if they light shield. The only way they can get out is by possibly buffering, buffering jump will get them hit, buffering spotdodge will leave them vulnerable to the next shine, and buffering a roll may not get them away, but if they do you can punish rolls pretty well. Just ask Shiz. He was telling everyone he plays "don't roll" on the stream during apex.
Thanks for reading! Thanks for the sticky and post any suggestions or questions below