Ice Climbers "desynch" in Ultimate
Solution 1:
Fair warning, I don't really play Icy's but have a friend who does pretty competively.
Basically, you will need a controller set up that allows you to buffer b, while doing falling nairs, or rising nairs. So let's look at this first:
Controller
• Bind a bumper to jump (left is what I usually see, but i use right with Fox because it's easier to shorthop aerial)
• Bind a default jump (X or Y) to your shield. This will give you easier access to wave dash back to the ground to help with speed
• Bind your c-stick to tilt attack - Makes all you're aerials 1:1 input (ie: up on this c-stick is now up tilt or up air, etc..)
Once you have the controller set up, you can look at the buffering method.
Buffering Method
First option is to buffer your grab, when you miss, forces nana to use a special attack. Your input would be something like this:
Special(B) - (Hold Z in the first couple frames of your special) -> (In the first 3-5 frames of your grab animation) Directional Special
This desync will allow you to put pressure on your opponent in neutral, while they are trying to come for advantage
Your second option is to desync off your aerial, this is going to allow you to put more aerial pressure down. You can desync off the aerial by having Popo land in the start of an aerial and have nana land in the recovery of an aerial
This is a little harder, and one of the reasons you want to make use of your jump + cstick. Here's what you want to do: Popo should fastfall his jump so he can land in a falling nair/fair/dair/uair. Whichever one you want. While Nana is going to perform a rising nair/fair/dair/uair.
Essentially the input would be something like this:
Jump (bumper) -> Down on the joystick to start fast fall -> cstick direction for aerial
IMMEDIATELY followed by Jump (bumper) + cstick direction (causing a rising aerial).
Upon landing, most people will have Popo use a side special, while Nana comes down with a dair . It should desync the attack so you have 2 hitboxes.
I could be wrong, but I think theres a wait to buffer nana's taunt into an attack. If you land a freeze after a grab, you can force the chain grab (don't know the inputs for these though.)
Solution 2:
I've been following the guide here, with actual moderate success. Note that I have very little experience playing IC, but I was able to reproduce the desynch noted in the video semi-reliably.
As he notes in the description:
INPUTS:
Shield + Attack, then let go of Shield but hold down Attack. Better method is to Shield + A&B with A&B Smash set to on, then let go of Shield but hold down A&B. This way Nana charges a Smash and you have all the time in the world to desync. The first method has Nana doing a Jab, where you need to react rather quickly to successfully desync.
WHY THIS WORKS:
In Smash Ultimate, there is a hold buffer. When you use the move, the buffer ends. For example, if I charge a Smash then hold B, when the Smash ends the B move will come out- but only once.
Now, in Smash Ultimate, only Popo has the ability to grab. If you are holding shield, then press and hold A, Popo will grab thus removing any buffer for Popo, but if you hold A you continue to buffer for Nana since she hasn't performed an action yet! So now if you let go of Shield, Nana performs this A move.
So what else can we use to cancel a buffer for Popo, but keep it for Nana?
Our only limit here is that the input you do during shield must cause a shield grab to occur. By doing this, you cancel Popo's buffer but keep Nana's buffer. If you try to hold B after shield grab, for example, you are providing a new buffer for them both.
Turns out, a lot of buttons will initiate a shield grab. My preferred being A+B! With A+B Smash on, this will cause Nana to buffer a charged forward smash, making it the easiest and most consistent way to desync without even moving! You can also use tiltstick in any direction, or A + any direction, or A&B + any direction to buffer directional attacks.