Resident Evil Revelations 2

This method takes less then a minute for each kill using the retry option.

While playing the first part of the episode as Claire and Moira you will be wandering the corridors after the mysterious woman has spoken to you about the bracelets. You will eventually come to an area where 2 enemies come from 1 door *DO NOT go around the next corner until you have killed these 2*

Make sure you are Claire and have your Shotgun fully loaded after killing the 2 enemies and as you turn the corner an Afflicted will leap through a window in front of you as he hits the floor pump both shells into him and despite him being on the ground the tracker will count this as a mid jump kill. It's important you don't allow him to move or it won't count so you need to shoot fairly quick to get him down. Have your tracker up and you will see it go up despite him clearly not being in mid air, then simply retry and you will be back slightly before the flying Afflicted and you can just rinse and repeat until the Achievement pops.

*You can of course use an explosive bottle to kill the Afflicted, whatever works best for you*

Here is a video showing how to get the Achievement.

Just before you leave the facility you have to fight off lots of enemies. Kill them and let Moira opens the door. Two enemies will keep respawning in the cell block.

You will have to order Moira to stay in the other room or the zombies will attack her instead of you.

Once this is set up, you can take your time killing them in mid-air. Everytime you kill one, another will spawn in his place which makes this a perfect place to shoot down the 30 enemies.

Adding to solution 1 above, I recommend Living Dangerously and running the gauntlet past the three lurking enemies to get to Mr. Window Leaper almost twice as fast for the shotgun BLAST I had level 4 damage equipped on my shotgun and it killed real good