Advance Wars 2: Black Hole Rising/Duty & Honor (Hard)

First of all, check out and remember the laser pattern, to make sure your units are safe.

On the very first turn, the lasers will not shoot. Therefore, deploy your units to the right as far as possible, keeping the tanks and medium tanks in the front. You can send your rockets north to destroy the left laser, and your mechs through the mountains to raze the right laser.

Afterwards, keep in mind the lasers will shoot not every turn, but every 2 turns, hence you will always have a turn to attack without being at risk.

Pushing aggressively with Kanbei's medium tanks and CO power will eventually defeat Adder's weak army, and you'll be able to reach the cities before he manages to capture them all.