Yea, the trick is that some of the upward arrow blocks are fake, they can be spotted on the minimap easily because those sections are in a different colour there.
For the clams, pretty sure the key is using the slow-mo ability (mapped to "7") combined with the dash-slide near the top. I don't know if boost ability (mapped to "B") is absolutely necessary or optional, but it doesn't hurt to use both. In my impression the timing is very tight for this, so I am still not sure if I am actually doing what is intended, or am I still missing something obvious to make it easier.
In any case, losing characters to insta-kills like that doesn't actually cost any mana to recover them after the screen transition, so the first screen is a free-pass anyways (2 mandatory clams, 2 spare characters), only the second screen requires at least one successful dodge as it has 3 mandatory clams.