Shadow Warrior

In Ch. 16 you should be facing a bevy of weak enemies on a rope bridge. SAVE before you engage them. (Make certain prior to the encounter you have the Shockwave ability unlocked). Now, they should all form a line or cluster on the bridge as there is not much room for lateral movement. When you are certain that you are aligned with them, use Shockwave, repeatedly if necessary until they are all knocked down. Now as they are down, fire a rocket from your launcher. If done correctly, this should garner 10+ kills. Reload your save. Rinse. Repeat.

Cheers.

(I have played this section on the PC version, hence why the achievement is not yet unlocked for me. But would I mislead you? )

For this achievement you'll need to unlock Shockwave with a Ki Crystal in the Powers menu. Shockwave is activated by hitting ++ it will knock the enemies in front you down to the ground for a few seconds. Upgrades can be bought to increase the stun time and area of affect.

At the very beginning of Chapter 17 you'll be running up a long stone pathway that is crawling with 30-50 skeletons and demons. As you make your way up this path get a large group of them in front of you and use Shockwave. You can use any weapon you like to kill the ones who are stunned and on the ground. I used the shotgun so I could focus on killing the stunned enemies and not blowing up the ones still standing.

This level is also good for grinding a bunch of other achievements that require x amount of kills with certain weapons or conditions.