For the multikills, you want rampage, so the haunted forest AR (origin story reskin), or even origin story. Exotics, Cerberus. Issue is you need multikills, and most ARs and tanky enemies mean you constantly run out of ammo before you get 2 kills. ARs are in a really bad place and you feel a detrement to your team. Don't worry about motes, just get the multi kills + AR kills as fast as possible, play normal gambit too, not prime. You'll be at around 15-18 games of the 40 needed, when your done. Then do your last games using anything but ARs. Newsflash tho, breakneck is an AR, so currently it's not good