- this trophy has be earned on the Shanghai mission
- i recommend to do this on easy
- after you get out of the elevator go to the weapon crate and equip an powerful weapon like a shotgun
- for a multi-kill you've to kill 2 or more enemies at the same time (it will show up on the screen if you've done right)
- for this try to throw grenades at groups of enemies
- another thing that'll work, is to throw a grenade at 1 enemy, when it explodes, kill directly an enemy with your shotgun (this will also count as a multi-kill)
- in this video i got this trophy on the roof of the hotel
- if you haven't earned it so far, there are several other situations till the end of the level where you can get multi-kills
good luck :)