Destroy All Humans' campaign finale mission will pit you against two boss fights which are much more difficult than any other part of the game. The following guide will focus on the first boss, Roboprez.
Before we jump into the fight, we recommend that you upgrade your saucer as much as possible to make things exponentially easier. In particular, focus on the laser beam, the health of your saucers, and the power of reflection to return missiles at who fired it. There is no checkpoint system here, so if you die during any of the three phases, you have to start over from the very beginning.
Once you've spoken to Silhouette, she'll bring Roboprez. Immediately turn and go to your saucer. Avoid the fire he shoots you down and enter.
This first phase is not too difficult. The biggest threat will be the mine balloons he calls for. When you see him do that, shoot them first. The rest of his attacks in this area are easily dodged and rather weak. It can fire a flurry of gunfire in your area or start dragging a laser around your area. Just avoid these and keep your laser shot in the middle of his chest. This is its weak point and hitting it at least once will give you the optional objective for that part of the level.
If you find yourself running low on health, there are vehicles to the right if Roboprez lets you zap energy, or one of the giant mechs (which now appear tiny) will shoot you. Whenever you see these guys, we recommend that you zap their power and don't destroy them instantly. They can grant quite a large amount of health before being destroyed, and their fire won't hurt you too much.
When you lower Roboprez's health, he momentarily drops to his knees. Save your ammo, it can't take damage during this time. The moment he gets up and starts running, you may start hurting him again. As you move forward, sonic boom ammo is scattered along the path if you prefer to use it while it runs. It will stop just before the bridge. Before you start hitting him again, destroy any nearby SAM turrets and any mine balloons he summons again.
This is where things start to get complicated. Hope you upgraded your Reflective Blasts to at least activate faster. When Roboprez raises his arms, he will start firing pursuit missiles at you. It will also do this continuously if you stray too far for health or something like that. If you've fully upgraded the Reflect Power, it'll send them back to doing a bit of damage to it while you're gearing up. Make sure you keep destroying the mine balloons when called out and dodge his other fire as much as possible while hitting him in the chest with your laser.
If you're in poor health every once in a while a mecha kicks in to pick up some health, but that was very inconsistent for us. There are vehicles on the bridge that you can skip, but like the previous cars, they won't give much health. Continue the above procedure until he gets back to his knees.
Once Roboprez gets up, he will turn around and start running across the bridge and stop in front of the Pentagon. Again, there will be sound boom ammo if you want to shoot him. Make sure to remove the SAM turrets and mine balloons surrounding Roboprez again. In this area, it will release the most fire and summon the most balloons. If you don't watch your health, it will decline quickly. The good news is that not much needs to change in the form of strategy. Unfortunately, there isn't much of a chance to get healthy here, so avoiding the fire here becomes even more important. His attacks will now reach much further and his laser beam can be especially difficult to dodge with the magnitude of the blast.
Stick to the plan of shooting your laser beam into his chest while dodging everything else, and you'll end up knocking down Roboprez for the last time and getting ready for the game's final boss.
