A group of Engineers asks you to fight on the Blasteroid Map against Geth . If you want a decent score, opt for Elite Geth where you will fight Pyros, Hunters and the like.
Even on Insanity, this one isn’t so tough. Blasteroid, as mentioned before, is a good map, especially for snipers as you can use the towers up high to rain fire on your enemies. The best squad to take is EDI and Tali or Garrus because Overload and Sabotage work wonders on Geth.
The only things to worry about are the Hunters so keep an eye on the spawn zone. Make a note of their position and take them out as soon as possible. There are also a few Rocket Troopers who could potentially pose a problem but if you close the distance, unleash tech powers and bullets, they will crash and burn in no time.
If you manage to rack up killstreaks you can score in excess of 6000 points in this match. You should look to unlock Reapers or if you obtained a Gold token, purchase Reapers, Super Elites or the No Medi-Gel Modifier. Check your mail again to unlock more challenges and to be given the SMG Power Magnifier reward.