Call of Duty: Black Ops II

Single player Story related, this cannot be missed,

you will get this at the end of the third mission no matter what difficulty you are playing on.

Mission 3 - Old Wounds

Mission Challenges:
1) Eliminate 15 enemies with the pulwar sword - Simply melee kill 15 enemies the pulwar sword. You will find the sword in a skeleton of to the right at the beginning of the mission.
2) Destroy and enemy helo with a mortar - You will be able to find mortar rounds in a locked room after the meeting with the Afgans. When you begin your horseback journey to battle, a troop transport will be near the ground, chuck a mortar round or two at it to complete this challenge.
3) Use the secondary fire function of the Stringer launcher to kill 25 enemies - The stinger can be found on the same roof of the mines. You can sit on this roof and farm the kills as there will be constant reinforcements until you destroy both BTRs in this area.
4) Destroy 4 enemy helos in the North Pass – This will be priority one after you detonate the cratering charges. When you get on horseback again, head to the left where the BRTs and Tanks are coming from. On the hill, you will be able to see helos off in the distance. You will need to destroy 4 of them.
5) Run down 10 enemies while on horseback – Simply run over 10 soldiers while or horseback. There are plenty of them running around the desert for you to take advantage of.
6) Destroy an enemy helo with a truck mounted MG - There is a pickup truck with a mounted MG in it near the ammo cache you need to secure. There will also be a few helicopters flying in this area.
8) Destroy an enemy helo without using the stinger lock-on feature - This can be done in multiple areas of the mission. It is best done after you destroy the 4 helicopters in the North Pass.
9) Collect all 3 Intel – The first Intel is located in the room where you meet with the CIA guy, the Afgan, and Zhao. It is to the left of the table that has the map on it. The second intel is located near an ammo supply point in the area between the 4 passes. The third Intel is located near the ammo cache that needs to be secured. There will be a small cave to the right from where you enter the pass and it is laying on the ground.
10) 100% survivability - Complete the mission without dying or failing a check point.

When you reach the interrogation of Krevchenko, Mason will start seeing number and want to shoot him. Make sure you keep tapping X to prevent this. Later on in the game, the decision here will affect earning an achievement in a later mission.