I stumbled my way into what I assume was a single player skirmish mission, to my surprise I unlocked the flanking achievement. I had to find out what I actually did to unlock it later on though, and it's ALL in Japanese.
As for everything else... I am clueless.
100% Achievement Points: Retail
Oblivion, King Kong, Condemned, Cars, Eragon, NBA 2K6, NHL 2K6, Bioshock, Two Worlds, The Incredible Hulk, Iron Man, Spiderman: Friend or Foe, Fantastic Four: Rise of the Silver Surfer, Superman Returns, Dead Space, Fallout 3 (PC, 360), The Force Unleashed, Spiderman: Web of Shadows, Risen, Divinity II, Call Of Duty 2, Tron Evolution (PC)
Watchmen The End Is Nigh: Part I