So, I finally figured out a way to get the “That Won’t Save You” achievement in Castle DLC (Assassinate a player with their hardlight shield up).
See, I had an idea; I dropped into game of Extraction in Castle DLC, and offered myself up to the enemy team; basically, I walked backwards towards a group of enemy players and managed to give one of them a free achievement. I figured “do good things for others, and good things can happen to you in return”. And you know what? It worked!
Towards the end of the game, I ran into another Blue (I was on Red team), and as soon as he saw me, he threw up his Hardlight Shield. He let me circle around behind to assassinate him, and bam! Achievement Unlocked. That makes Castle the only Halo 4 DLC where I have all the achievements.
I noticed there weren’t a lot of people in Castle DLC using the Hardlight Shield, so I decided to try this out. If you’re having trouble with this achievement, give this method a try. Who knows, maybe you’ll be matched with at least one equally generous soul.
Same method. Thank you kind souls.
> No boosting please.
I don’t see what the problem is, not many people continue to play this game so it would be a bit harder to gain achivo’s when few people still play or even use Hard Light.
Hey. I used the same philosophy last night and it worked for me too!
Glad to see it worked for somebody else, too. 
I had a similar experience. I had no faith in the Halo community, and after 3 days of somewhat solid playing in the Castle playlist, I hadn’t seen a single hard light shield. Then one day, somebody just threw one up in front of me. I stopped shooting, ran around behind them, and to my surprise they stayed still and let me get the achievement. I sent them a thank you message, and since then, I have carried a shield in most of my games, trying to give at least one person that achievement every game. Pay it forward Spartans!!
That’s all very heart warming, but this is still a -Yoink- achievement. People rarely use a HLS, so it’s almost impossible to get this achievement “legit”. 343 should just STOP with the multiplayer achievements. They sucked in Reach, and the suck now.
> > No boosting please.
>
> I don’t see what the problem is, not many people continue to play this game so it would be a bit harder to gain achivo’s when few people still play or even use Hard Light.
Number of people playing is a non factor. You still find games as fast as any other, and all that matters is that someone is in your game lobby.
> No boosting please.
Did we boost? This achievement isn’t even close to causing a hindrance to someones gameplay. At least not widespread. Besides isn’t the achievement itself influencing people to do these things. Surely this boosting thing works both ways in terms of potential harmful affects. Specific matchmaking achievements are ridiculous. It forces people to change their playstyles if they want to get that achievement which I did. If anyone did a worse thing it’s the creators of this achievement for only allowing me to get this achievement through MATCHMAKING and by changing my playstyle. That’s not right.
> No boosting please.
I don’t think this really counts as boosting… and it’s the only way I know of to get the achievement anyway, since hardly anyone uses the Hardlight Shield in any playlist. So the only way is to encourage other to use it, and what better way than this? Give an achievement, get an achievement.
Awesome! Thank you OP, I will try this out!
However, there will always be that jerk who kills you before you can allow his teammate to go for the achievement!
> Awesome! Thank you OP, I will try this out!
>
> However, there will always be that jerk who kills you before you can allow his teammate to go for the achievement!
Indeed. I actually offered myself up several times, but some jerk on the Blue Team kept killing me before his teammate could complete the Assassination. I did give it to at least one of them, though.
Yeah, I should try reaching out to the people in the lobby through chat.
You know what. After the OP’s kind hearted story. I decided to help some people in the Castle matchmaking, I think I helped 5 people get it in one game.
I give out freebies, but everyone else does anything but assassinate me, and afterwards will -Yoink!- me. 
I’ve been using the same method for the EMP/Hijack achievement. Sadly, anytime I go for it though, they always hop out of the vehicle.
I did this too, got it within a day!
I think I will give it today. Maybe somebody will be generous as well.
A gametype where everyone has HLS as AA would be better for this, tough.
Can anyone with authority tell me…well…I KNOW it is a thin line, the one separating boosting/cheating from 4 or 8 guys who agree on doing something for mutual benefit, so…what is “legal”?
I mean, if I gather 6 friends/players-who-want-the-same, is it “OK” to go for an achievement?
If not “ok”, then, how illegal is it?
Again I dont want to cheat!
(However, I understand that even gathering people do do this is considered by some “conservationists” as something like a mortal sin…Thats why I ask to anyone with authority.)
> Can anyone with authority tell me…well…I KNOW it is a thin line, the one separating boosting/cheating from 4 or 8 guys who agree on doing something for mutual benefit, so…what is “legal”?
> I mean, if I gather 6 friends/players-who-want-the-same, is it “OK” to go for an achievement?
> If not “ok”, then, how illegal is it?
>
> Again I dont want to cheat!
>
> (However, I understand that even gathering people do do this is considered by some “conservationists” as something like a mortal sin…Thats why I ask to anyone with authority.)
For a while, the official stance has been :
“As long as every player that is connected is actively participating in the match is moving around, getting kills, and not negatively impacting the match for other players not participating in ‘Achievement Hunting’, do what you will”
This means you should :
Have enough players (with or without guests) to fill the WHOLE lobby, so no ‘outsiders’ can join the game and be negatively affected.
Every single player listed on the leaderboard should have some kills next to their name. If the system picks up on a bunch of guys standing around idle, with no kills, and multiple deaths, the system will tag you for ‘AFK players’ and dole out a matchmaking ban.
Thank you, sir, you made a family of Halo lovers very, very happy.
Azrael & MataHari
PS: Now…where is that list of friends of mine? 