Earned a Killionaire medal in Firefight.
An easy achievement to nab while using the GRCHEEVOS gametype in firefight, you need to kill ten enemies within four seconds of each other. Simply go nuts with unlimited ammo on a crowd of grunts and you’ll get this in no time.
Used a Health Pack to replenish life after taking body damage.
During the second mission, one of the first buildings you reach after driving the truck – not, if you were after the achievement of course- will have health packs on the wall. Simply use one up and feel 5 gamer points better.
Completed the 8th mission on Normal or harder.
Simply complete the 8th mission on any difficulty higher than easy.
Scored 50,000 points in a Firefight game.
Using the GRCHEEVOS gametype, you can simply just keep on killing and killing until the score counter in the bottom right reaches 50K.
Completed the Campaign on Heroic difficulty.
If you are a true Halo player then this is the difficulty that you started the campaign on. See it through to the end and nab yourself a deserved 50 points.
Completed a Firefight set on Legendary without dying.
Using the GRCHEEVOS gametype, set the match to one round and set the difficulty to legendary. One set will be 3 rounds of 5 waves with an additional Bonus Round at the end. It will take about 15 minutes to complete but once you do… 25 Points.
Completed the Campaign on Legendary difficulty.
This achievement is for the truly masochistic. Take your time through the campaign on this setting and the 125 points will easily be yours. Ok, not easily – but it will be yours nonetheless.
Scored 1,000,000 points in a Firefight game.
Using the GRCHEEVOS gametype file, simply keep on killing and killing and killing some more. To get one million points, it took takes about 90 minutes to reach it.
Killed 3 of the anti-aircraft batteries during the 8th mission.
In the night time flying mission over New Alexandria, there will be multiple anti-aircraft turrets set up on the rooftops. You can just fly around until you see the blue-ish white gunfire from them and then take them out. It’s easy enough to find three and killing them is even easier.
Performed an Assassination against an Elite to survive a fall that would've been fatal.
Right at the beginning of Mission 10: The Pillar or Autumn, you will come to a ledge with an Elite and some grunts shuffling around down below. To get the achievement, you need to wait for the Elite to come closer to the ledge and then run and jump off using Sprint. Aim for the Elite’s head and be sure to turn off the sprint on the way down. If you don’t turn it off, the achievement won’t work. When you are right above the Elite, hit the right bumper and pull off the assassination.