After mythic turns on, it's better to have 2 choppers driving around instead of a hog. It just takes way too long to kill brutes with this skull on. Choppers get it done much faster, and there isn't too much added risk if you're good with 'em. I got the achievement yesterday with 3 choppers and a laser user. At one point we had 32 extra lives. It only ended because someone needed to get off so we all died repeatedly. To handle black-eye, just work together to isolate grunts/jackals, hop out, melee, and get back in. It took us just over 2 hours to get the achievement.