Vidmaster Challenge: Annual

Vidmaster Challenge: Annual is a new achievement where you have to complete Halo after 9/25/08 on four-player Legendary Co-Op with the Iron Skull activated, and everyone in Ghosts .

It has been announced that while the Vidmaster achievements do not give you any points, they are worthwhile for some mysterious prize when you get all of them, although this cannot be accomplished until the Mythic Map Pack is released. The following statement at Bungie.net confirms this:

''Let’s dive into this a little deeper and try and address some of the questions that will no doubt arise from the community. First off are the “Vidmaster Challenge” achievements. These three will not earn you any gamer points but there will (eventually) be a pay-off. We’re not going to spoil the fun just yet but suffice it to say that gamerscore isn’t everything. There is a pot of gold at the end of the Vidmaster rainbow and it is something you will want. More details later.'' - "SketchFactor"

The only way to get Ghosts in the mission, is to actually have 4 people playing the level with the Iron skull on, without these, the Ghosts do not appear.