"Caboose, provide cover fire with that tank !"
"Okai !"
"And don't shoot me this time."
"Okay !"
-Blam-
"Son of a -blam!- !"
"Wait, what was the first part again ?"
Porcupine: Stick a Brute Chieftan with a Spike Grenade. 5g
Shotgun !: Kill 15 grunts, all with headshots in the passenger seat of a warthog. 15g
Gold Betrayer: On Legendary, allow a gold hunter to kill it's partner with it's cannon. 30g
"The Blacker the Core": Incinerate 5 Brutes, after you take off their power armor on legendary. 20g.
A Real Friend Would Argue: On Firefight, attack the same target your friend shoots 3 times. 5g
Keep going through Hell: Complete Legendary Campain with at least 4 gold skulls on.
"Never Give In !": Kill 7 enemies while your visor is red from damage. 5g
"Wiseass": As Romeo, shoot 14 enemies in the crotch with a sniper rifle and kill them. 5g
Naive Rookie: As the Rookie, throw a grenade and kill an enemy with debris. 5g
Care to Dare ?: As any ODST member, when Dare gives you instructions, ignore them and follow a different path to victory. 10g
Path of Destruction: As Dutch or Mickey, destroy 2 Wraith Tanks and a Banshee. 5g
Then It Hit me !: As the Rookie, survive a melee from a Brute on legendary. 15g
Buckin' Bull: As Buck kill 3 berserking Brutes without taking damage. 20g
Oh Mickey You So Fine...: As Mickey, destroy both turrets in a Phantom.
"Oh Romeo !": Save a female ODST from impending doom ! 5g
"Medic !": As the Rookie, use all the med-packs in the entire game. 10g
Just passin' by: On the back of a mongoose, kill three enemies with one rocket on legendary. 10g
"Feet First into Hell !": Jump into a fire on the ground, via firebomb, flamethrower, or natural. 5g
"Firefly !": On Firefight, kill ten drones via inceneration. 5g
Chicken Noodle Soup: Kill 5 Jackals on Firefight. 5g
"Who Cut the Cheese ?": Knock off 5 methane tanks off of grunts.
ODST Ninja: Kill 20 enemies with your silenced weapons or assassination. 15g
That all I can come up with so far...