Is it bugged? I tried it several times and always got four branded but it did not count.
I don't think it is bugged. I got it successfully yesterday.
Ok thanks, I will continue trying it.
I thought it would be strange that I didn't get this one the first time around because I was using the spear pretty much off cooldown. But I went back in today and when the branded spawn after grabbing the spear, I waited until they were all grouped up nicely and managed to get it right away. It took a couple of seconds after the strike for the achievement to pop up.
Bloodcovered Backstabbin' Blackjack the Blade, at your service.