While the game is loading, hold Start on controller 2. Keep it held until the Main Menu appears. Now press L1, R1, R2, L1, Select, Start at the Main Menu. This will unlock campaigns 2 and 3 and activate cheat mode.
Now enter these cheats on Controller 2 during gameplay…
TriangleGod mode SelectLevel skip CircleUnlimited power XAll items R1More structures R2More units UpIncrease unit strength Right Decrease unit strength DownComplete current research
Thanks to Revolution reader BRBgk316!