No. Do them with friends, or by yourself. Turn on 4-5 of the easiest skulls, do it on normal, and you are good to go. PROTIP: Flood don't throw grenades, but you still get the multiplier for the catch skull
Yeah, Kapura is right. You are better off doing them alone. Just to let you know from personal experience, it is going to be harder alone, but then you have all of the points to yourself. :squirrel_rocking: No competeing with anyone else to make sure you get all of the points needed for the achievments.
Me and my friend have been doing that... we just pick whoever wants to get the achievement first and then let them get the 15k or 50k points and then hide while the other does the rest of the level.