1st phase
Crit works fine. So does weakness. Just cant first turn it since def is up. Design your team to kill it on the 2nd(and 4th turn if necessary) while it has def down. First team with 570 speed will hit it.
Japanese wiki says a full solar team can one shot it as well
2nd phase is where you want a defense/debuff/counter team if you're so inclined. Something that can take hits from those rocks.
I used another crit team with RR and negate with turn based damage to come in midway in the second.
The third phase is the easiest goes down fast with crit.
If you have RR and Yarrow and turn based damage with favorable RNG, it can take the whole mission