The recommended active skulls for this mission are Tough Luck, Catch, and Fog, but mostly Tough Luck. Tough Luck sacrifices the full potential of your grenade arsenal, and EMP/Headshot kills will be tougher to win, but in exchange for a reasonable multiplier. As for Fog, the battles in both Lake Beds could be a bit awkward, and you'll need to be extremely methodical during the final battle to hunt down Grunts and Jackals. With Catch, Factory A and the warehouse are more difficult, but Catch is an invigorating addition if you're not aiming for speed.