Vidmaster Challenge D Achievement
Vidmaster Challenge D10
Complete Operation D, Mission 6 with the Famine and Thunderstorm Skulls active
This isn't too hard, although I recommend buying the Damage Boost upgrade.
Equip both skulls before the mission. You might find yourself low on ammo, but there's a trick. There are weapon crates on the top right and top left, both by the pillars, and on the left side between the top left and bottom pillars. These weapons (Battle Rifle, Assault Rifle and Shotgun) spawn near instantly so you can get a full weapon. Also, if you just stand near the crate while firing, you essentially have infinite ammo.
Pass the mission with the skulls on for this achievement.