Figured I'd post here, because I don't know if the other desync guide is updated.
Did some testing on desync ice blocks. Measured frames from start of desync to first frame of ice block startup. Spot-dodge took 34 frames, roll takes 39, and optimal dash dance desync comes out in 28. For the dash dance desync ice block, you dash one direction (3 frames), dash opposite (3 frames) and then let go so nana doesn't skid, and if you input an ice block 7 frames before the end of the dash animation (frame 21), she will start an ice block at the 28th frame and popo will just be in wait.
Fastest for popo ice block is still pivot ice block, where you input b on the 3rd frame during the turn animation which starts an ice block on the 17th frame.
Also there's a 1 frame window after a full hop where a b inputted the 4th frame of landing will result in nana only ice block (or blizzard) on the 10th frame of popo landing. This also works for platform fall through landing, but I can't seem to get it to work with short hop or short hop fast fall.
Lastly, you can shield with one ice climber and continually b with the other if you press b on the last frame of the previous move for popo or 7 frames before the last frame for nana. @
BigVegeta showed me this with holding z. This causes popo to grab then light shield and nana continually grabs. If you press b 7 frames before the end of the grab, nana will ice block, then you press b 7 frames before the end of the ice block (54th), etc. You can also do this with plain shield and with popo inputting b instead of nana. Blizzard also can be input, but it will also cause the shielding climber to spotdodge or tilt shield down.
The point, I guess, to get out of this is that
the fastest way to get a nana ice block out of a desync is the 2-dash dash dance desync (as opposed to the 3-dash desynce you use to get a nana blizzard), and I imagine there's a bunch more 1 frame IC desync stuff, that a really skilled IC main might be able to implement. I'm surprised I haven't seen the 2-dash desync more as it allows ice block without committing to a spotdodge/roll. You commit to a slight move forward, but you do that with the blizzard dash dance desync as well.
EDIT: another 1 frame desync is a turnaround desync with blizzard input on the 20th frame of the dash animation. This seems weirdly easy to me as opposed to the others, I can get about 1 in every 8 tries.