DLC's in Halo Reach came with some new achievements. As the game became less popular and currently there are no dedicated queue lists to play only on the new maps, some of the achievements became really difficult to get as some of them require that DLC maps.
Usually, when playing on matchmaking, you never get that maps to vote as all the players must have the DLCs in order to get the possibility to play them, and the few moments when that strange thing happens, no one votes the new maps so you can't try to get the achievements. What it's more, even if you manage to play in a new map, you need to do the thing the achievement requires.
I recently discovered that I have only 4 achievements left to "complete" the game, all DLC multiplayer ones.
How can I increase the possibilities of playing in a new map? Can I create a custom online map with friends to get them?
Best Answer
Your best bet is to get a party of people who have the DLC that's large enough to fill the matchmaking lobby. If you don't have enough friends (or controllers) with the DLC to pull this off then you can look to one of the many achievement websites to try and organize a boosting session with their community. I would recommend TrueAchievements.
Be warned that 343i is opposed to players being idle in matchmaking, so if you do have controllers with no player make sure that they get at least one kill per game or you risk being banned from Halo: Reach matchmaking.