Halo 3 Campaign Meta-Game Achievements?

[Galeon]

How do you get the Campaign meta-game achievements ( Guerrilla,Demon...etc ) .......i tried it on co-op do you have to get the points total or separate?........and what are some of the strategies for this?

 

[Swift Panther]

You have to get a separate score. I did it on heroic and I turned on skulls most of the skulls. The harder the difficulty and the more skulls you have turned on the more points you will get. You also get extra points for headshots, sticks, melee kills. Try to complete the level before time multiplier runs out.