Vidmaster Challenge: Déjà Vu

Vidmaster Challenge: Déjà Vu is an achievement in Halo 3: ODST and one of the Vidmaster Challenges. It is unlocked when you complete Coastal Highway on 4-player Legendary Live co-op, with Iron skull activated, and not using the Warthog or Scorpion at all. It is worth 25 Gamerpoints.

It is represented by a green Marathon symbol, with the Iron Skull in front of it and four white stars surrounding the Iron Skull.

Strategies and Tips

 * At the beginning of the Highway, there is a tunnel that leads underground. You will find four Rocket Launchers, with 1,000 rockets (2 loaded in the Rocket and 998 on reserve), and two Mongoose's. These only appear by putting the Iron Skull on Legendary.
 * The Rocket Launchers mentioned above have special properties, allowing you to carry a rocket launcher from the first part of the level and the 1,000 rocket version, implying that these were specially made to make this very difficult achievement easier.
 * If there are Banshees, try to get off your Mongoose and destroy them when they move to you.
 * Try to stay behind the Oliphant.
 * Don't rush the level; try to stay back and destroy the Ghost's and Banshees before moving in.
 * Do NOT tell Buck to exit the gunner seat of the Warthog, as it will prevent you from getting the achievement. However you can throw a grenade underneath the Warthog, which will prompt Buck to bail out. He will follow you, but if you find a Rocket Launcher, or even better a Fuel Rod Cannon and equip Buck with it, he is a very powerful ally. If he rides on a Mongoose with you, he is very very helpful at taking out Ghosts and Banshees. Also a Fuel Rod Cannon can be found on a dead Grunt;after your first battle on the highway right before the first door.
 * A charged Plasma pistol will help you hijack Ghosts if you're close enough. Be careful, if you attempt this the EMP does not disable weapon systems.
 * Try hijacking an Anti-Air Wraith, it may take some time, but is worth it due to it's high rate of fire and increased damage.
 * If you are having a problem getting a checkpoint when you open the gates of each section, make sure that: Everyone is close to each other and in the gate at the same time; You are not shooting at any covenant and they are not shooting at you; Dare are has not moved completely out of the gate. A Cooperative checkpoint is not the same as a normal Checkpoint (Cooperative Checkpoints are where you start the level from if you save/quit).
 * Grab a health pack and regroup at each checkpoint. If your Mongoose is heavily damaged, grab a new one that sometimes appear in each checkpoint.
 * Although walking the whole level is nigh impossible, if you find yourself stuck on a certain part, try getting off your mongooses or ghosts and walking. It is easier to aim, easier to see, harder to be hit, and you will have twice the number of rocket launchers firing. As long as you can deal with threats to the Oliphant quickly, walking the section is a valid option until it is completed.
 * For the passage containing all of the drones (the 2nd or 3rd), it is helpful to keep the SMG to deal with them, as hitting them with rockets can be quite difficult.

Trivia

 * The achievement is named due to its similarity to the previous Vidmaster Challenge achievement Annual, which also requires the Iron Skull, 4 player Legendary live co-op play, and finishing in a light vehicle (as walking is not suggested due to the Oliphant being faster, and on legendary can be destroyed in a matter of seconds from enemies).