Déjà Vu shares many similarities to the original Metal Gear Solid. You goal is to recreate scenes from that game. As soon as you complete one flashback, you're free to end the mission, but we'll show you how to finish them all. To keep things simple, we'll walk you through them in the same order as they appear in iDROID.
Make your way from the prison camp to the heliport and further on to reach the helicopter sitting there. Take cover and then look at the front of it. This will trigger the first flashback scene of the Hind D sitting on the heliport from Metal Gear Solid.
Right beside the Hind D is an empty helicopter landing pad with a box in the center. Snag the grenades from it to trigger the next flashback. Just be careful of the roaming guards and intrusive spotlights.
Not too far from where you are now, there's a red door with a security camera next to it. Head towards the door and find some cover opposite the camera. This will trigger the next flashback scene. Just be cautious not to get spotted by the camera.
Go through the red door and move toward the underground section of the admin building. When you're inside, take your next right where the flashing light is located. Go forward into the next room where the boilers are, look right and you'll find the Easter Island head sitting there.
Head back to the camp settlement next to the cliff side where you began Ground Zeroes. Next to the campsite, you'll find some grenades and C4. After gathering up both, throw a grenade into the open hatch of the nearby armored vehicle. This will trigger another flashback, the boss fight with the tank and gunner.
Head back to the heliport and jump into the Jeep near the Hind D. Drive it towards the underground tunnel in order to trigger another flashback, Metal Gear Solid's finale between Liquid and Snake.
In order to finish the final flashback, head through the red door we spoke about earlier. Move forward until you see a set of transformers behind a fence. Go to the gate, pick the lock and approach the first transformer on the right. Turn the power off to trigger the final flashback, the fight with Psycho Mantis.
Move towards the air duct opposite the main gate of the admin building. Crawl into it to finish the final side mission. If you stick around to the end of the credits, there's a Metal Gear Solid quiz you can take.