OMG BFF FTW

OMG BFF FTW is an achievement in Halo Wars that is unlocked when you complete the entire Campaign on Co-Op. This can be done on any difficulty, and do not all have to be done at once, and not on the same difficulty. Just complete all missions Co-Op

The name of this achievement was obviously inspired by common slang terms used on the internet. When spelled out, it becomes Oh My God - Best Friends Forever - For The Win.