you cant upgrade it twice
No.
by going to the random box in zombies
It means you can upgrade your guns.
dual wield and shoots lasers. Its called Typhoid & Mary.
No, but if you complete the campaign you get another level on zombies called "Five", whereas you start off only having "Kino Der Toten".
Only in zombies.
No.
by going to the random box in zombies
It means you can upgrade your guns.
You can get it in the mystery box in Zombies.
disco stick
you get it from the random weapon box by luck.
by using the mystery box and getting lucky
you don't it is random
You get more maximum ammo when you upgrade the gun. The ak74u usually has 20 ammo, and gets 40 when its upgraded.
No, you can't upgrade a gun more than once.
you can't get it in multiplayer. you can only get it in zombies through the mystery box.