Halo: Reach Challenge Initiative - February 10, 2012

This doesn't take to long. Because there are like 15 waves in Arcadefight (only if you finish the match), and it only takes 20 minutes, I recommend doing that. This is because it takes 7 min. to do a solo firefight and only 5 waves in that frame of time. When you have 4 people, it'll go by WAYYY faster.

Challenges like this can usually be achieved in one sit down of play, so long as the numbers are reasonable, for instance, this one requiring 50 could be done in 10 games if you average 5 kills a game, or only 5 games if you average 10 kills a game, it all depends on your own skill level, Objective gametypes usually help since they have no kill goal, but eventually never seem to end if everybody is only killing, stick to Big team to have your team make progress while you help mow down the enemy

Ignore the guy above, play in invasion and you will always spawn with plasma grenades, don't waste your time looking for an elite slayer that's not going to happen.

Just play the level on legendary, and once you've killed all elites at the end, quit the game and reload it, then don't die on the mass driver cannon. if you do, just quit and start again!

Team SWAT or Team Snipers. Big Team Battle or Invasion may also be long enough to allow for 14 kills.