for the cursed thralls part, if you are a titan the shoulder charge can kill multiples at the same time. I somehow ended up with 3 kills via one melee kill. I'm guessing the others were close enough to take damage, but not damage me? For me I just kept doing the rasputin mission on earth. (the one that was the daily yesterday) that mission let me do multiple stages of this and do other bounties that are currently available as well. EDIT: what's the regret reward??