General RAAM will attack you in 'Pale Horse', the last chapter of the game. It is recommended you do this with a partner, as it's very tough otherwise.
I personally hid behind the first wall and unloaded my Longshot into his head until he got too close. When he did, I jumped over the wall and high-tailed it to the other side of the train for cover. Then I started unleashing some more headshots until he went down.
This video was not done on Insane, although it says it was.
For Co-op, your best method is:
- This achievement can be done on Co-Op. If done in Co-op, it will not matter who actually kills RAAM. The achievement will unlock for both players, assuming neither one already has it.
- RAAM is surrounded by Kryll that will harm you if you don't stay in the light.
- General RAAM must be killed on Hardcore difficulty to count. Not Casual or Insane.
- Directly before you battle RAAM, you are in a subway car filled with weapons. These respawn after a few minutes, so wait it out and make sure you have full ammo for everything you want to use.
- Check out our discussion thread on defeating RAAM here.