I might have found an easier way to get Improviser (Get 2 kills at once with something from the environment.)
First level on the ship when the game first tells you hot to do stealth takedowns. There's a guy standing at a computer and a large toolbox directly to your left. Grab it, thow it at him then jump into the hole in the ground a little further to kill yourself and throw the same toolbox at the guy again.
No idea why it unlocked for me when I did it this way, but I'll take it. I was going for Poltergeist achievement. However restarting the checkpoint erases achievement progress.
Thanks to Gackt