Vidmaster Challenge: Annual

Vidmaster Challenge: Annual is a Halo 3 XBL-exclusive achievement where the player has to complete the level Halo on four-player Legendary Co-Op with the Iron Skull activated, and everyone in Ghosts. The achievement is named "Annual" because it was only possible to unlock it after September 25th, 2008, one year after Halo 3 was released (give or take a day, depending on local time zone).

It is represented by a green Marathon symbol with the Iron Skull on it. The Iron Skull is surrounded by four stars.

Strategies and Tips

 * A way has been discovered to complete the challenge much faster. It is possible to skip climbing up the tower by climbing up the slant on the way up, jumping across and landing one floor up.
 * Even though all players must ride a Ghost, only one of the players is required to reach the end on a Ghost for all four players to receive the achievement. This does not mean the other three aren't required to ride Ghosts. If the players reach a replacement vehicle during the ending run, they may use it only if his/her Ghost is destroyed.

Warnings

 * Make sure that everyone doing the achievement is sure that they won't lag out of the game midway because there's nothing more annoying than having to restart the level after someone's connection messed up when you were almost at the end.
 * The only way to get Ghosts in the mission is to play on Legendary Co-op from Mission Start until the end. They will not show up if the level is started from Rally Point Alpha or if played on a Solo Campaign. There are four Ghosts directly under the ramp to the left as you exit the control room.
 * The Ghosts also have a major disadvantage against the Warthog: the ability of auto-aim. This problem means that some passageways guarded by carrier forms become almost impossible to access, attempting to speed past carrier forms is now impossible, because if your cross-hairs point at them you will lock on to them and drift towards them, resulting in damage to your ghost and, in fact, you may fall to your death. A good way to counteract this is to look up while you drive. However, you have a limited range of sight while you are doing this, so it is not recommended while tiles fall under you.
 * The flooring sections near the end will fallout from under the last player if your ghost group is not tightly packed enough. Use the interior hall sections to tighten up your formation before exiting - the timing of the floor tiles is based on when you enter the open sections, not total time in the mission.
 * Skipping the end cutscene may result in reverting to the previous checkpoint. It's highly advised to watch the entire ending cutscene.

Video Walkthrough
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Trivia

 * The Vidmaster achievements do not reward the player with points but if all the Vidmaster achievements are acquired then the player will be rewarded with Recon armor for online play. Though, the player must also own a copy of Halo 3: ODST in order to finish the Vidmaster achievements.
 * There were some cases of people getting this achievement on the 24th of September, because of time zone differences.
 * There are seven Vidmaster achievements; four achievements can be found in Halo 3 while the other three are in Halo 3: ODST.
 * Following the completion of this level the normal cutscene will be different. Instead of just a warthog, a warthog and a ghost will jump in the Frigate.
 * If you look at the background, there will be the Marathon symbol, which was another game made by Bungie. This is the case with every Vidmaster achievement.