i got mine t the mortar mini game lol. yeah you got to do it solo i think, i may be wrong. but its not hard. don't bother with 1 or 2 hallowmen at a time, just listen to jammer say where they are coming from and then target the 4-6 that are coming out all at once. and other big groups. if their gone swing to the other side of the map and maybe fire a shot on the way at 2 or 3 left over zombies.