Since there is no confirmation on what the achievements will be for the game, aside from the time being, let's create our own!
Here's some of mine:
"KEEP IT CLEAN - 10 GS: destroy all environmental objects within the city."
"Terminator - 50 GS: Never use a health pack"
"Ray Charles? - 50 GS: Never use the low-light mode, VISR"
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Stronger: Kill a Brute Chieftan with another's gravity hammer. 15G Mind Tricks: Use position to get an enemy to shoot another enemy for you. 5G Vidmaster Challenge: Humpday Medal: Tea-bag every species in the game (including fallen Firefight comrades) for a total amount of 5 minutes. 0G True Ninja: Take out a squad of Brutes 1 at a time without any of them noticing you there. 50G 2 For 1 v2: Get a 2 for 1 with a sniper, Spartan lazer, and grenade in Firefight or Campaign. 35G Just a city boy...: Play on all Firefight maps. 10 G Combat Evolved: Headshot 100 grunts with your pistol. 15G