Lets the investigation begin !

This is the strategy that I used to cleared the first phase:
?-1, ?-2: just let it go as standard setup, it's kinda easy.
?-3: top to bottom, 2-2-1.
?-4: top to bottom, 2-2-1. Put your fastest squad in the middle, then pray for RNG. Just be prepare that the boss is pretty strong with a heavy attack.

Also, the rare chest in ?-3 and ?-4 will give you Life Crystals.