Upon reaching approximately 60% health, The Colossus will activate a powerful frontal energy shield and begin deploying 'Seeker Drones'. The shield makes direct frontal attacks ineffective. Your priority should be to destroy the Seeker Drones, as they can quickly overwhelm your squad. Use SMGs or Assault Rifles for crowd control. The Colossus's weak points will now be exposed for a longer duration after it charges its 'Energy Barrage' attack. Use this window to deal significant damage. Consider using EMP Grenades to temporarily disable its shield, creating a brief opening for frontal attacks.
