This achievement for me is still glitched, now i know people say it can’t be glitched and it’s just about luck however i have spent at least 10 hours attempting this achievement, as it is my last achievement left before full completion. Is anyone else still experiencing problems with this achievement, i believe that for me it’s fully glitched although i know some people that have gotten it with ease.
Although it is really buggy it is still possible to obtain, I just got it a couple of weeks ago. It seems to me that the game is just really picky on how you have to do the assassination, as it took me seemingly forever to unlock it as well. How are you actually doing the assassination? What worked for me was sprint jumping off the cliff (assuming you’re doing this on the Package as well), stopping my sprint before I hit the elite and making sure not to keep my gun pointed at him and for some reason this counted for the achievement.
I’ve also had a look on a few achievement websites about this, and apparently you can also get it on Nightfall which seems to get better results, there should be a number of good videos for that on youtube. But as said before, it is definitely one buggy achievement.
If you are doing that assassination I like to call the fallsassination, where you assassinate an enemy while he’s on the ground and you’re in the air, you won’t get the achievement. You have to do a plain old assassin as soon as you fall on the ground. You’ll be practically dead, but you’ll get the achievement while assassinating him. It’s kind of a glitch. I did it in about my fifth try during my solo legendary run at the beginning of The Package.
What achievement??
Thanks for the feedback guys, I’ll have some more attempts today to see if I can get it, usually I’ve been trying on “the package” but maybe I should give it a go on “nightfall”, it’s just a shame that I haven’t got the achievement yet because it’s my last one for halo reach. Hopefully within the next few days I can achieve it based on the advice given to me, thanks 
i didnt have any problem getting this achievement. took me maybe 3 or 4 times
So I was replaying the Reach campaign today and noticed I didn’t have this achievement unlocked either. So I loaded up Pillar of Autumn, and after around an hour or so of frustrating deaths off that -Yoink!- cliff AND a few assassinations that somehow didn’t trigger the achievement, I finally managed to get an assassination and on the bottom of my screen the achievement popped up. Keep in mind I’m playing this on Xbox One, but regardless the achievement DID pop up on my screen. Then I go to check my achievement list and it isn’t there… it’s still locked. Unless if I have become schizophrenic or visually impaired over the past 24 hours and my eyes were seeing things when the achievement popped up right in front of me, then I can confirm 100% that this achievement is in fact glitched. Unfortunate to say the least lol