Gears of War: Judgment

To unlock this achievement, you must get 3 stars on all 42 sections of the game on the insane difficulty.

1) Play co-op with 1-3 friends.

2) Have the host be on insane and the joiners be on casual.

3) Have the people on casual do most of the work towards earning the three stars. On every mission, activate the declassified mission and get as many ribbons, gibs, executions and headshots as possible as these provide a sizeable boost to the star meter.

4) Once all enemies are cleared out of the section and before continuing, have all of the joiners quit out of the match so that just the host is left. If three stars were not attained, restart the section.

5) If three stars were attained, continue to the next section.

6) Invite your friends again once the new section has started and repeat steps 3-5 until all the missions are complete.

Overall, this should take about 8 hours per person

Here's a way for multiple players to get Onyx stars from a Declassified Mission while using the split-difficulty/dropping out trick. I've written the guide based on 2 players but it works fine with 3 or 4. This method can't be used in split-screen. Credit to LeiChat who confirmed that you can incorporate split screen players but that the split screen players can only drop out together (therefore you can't use this trick in a 2 player split screen game but can include split screen players in a 3 or 4 player game).

NOTES BEFORE YOU START
To speed things up I'd suggest everyone get into an invite only XBox Live party so that the person or people quitting out can rejoin the game without the need to send invites. Hopefully it goes without saying that the in-game party should be set to invite only.

1. Load the game from the main menu with player 1 (the host) on Insane and player 2 on Casual and earn the 3 stars. These will show as bronze stars at the top of the screen while earning them as player 2 is on casual.

2. When you get to the part where you have to press up on the D-Pad to finish the Declassified Mission player 2 should quit out.

3. At this point player 1 is in the game on their own with 3 bronze stars showing. Finish the mission by pressing up on the D-Pad and you'll be given 3 Onyx stars instead - YOU NEED TO STAY ON THE STARS SCREEN!!

4. If player 2 joins back in while player 1 is admiring the 3 Onyx stars then player 2 will also get the Onyx stars. Player 1 has to wait for them to see the stars and then continue onto the next section for them to count for everyone in the game.

Please Note
Just to let you guys know, player 2 (and 3/4 if you've got that many players) joining back in will join back in on Casual (or whatever difficulty they picked in step 1). They aren't given a choice about what difficulty they want to join in on. In addition to this I have no idea about what difficulty they'll be on if they join a game in progress that they've not played in before but since it has no impact on getting the star achievements I haven't bothered to find out.

What you get
Player 1 gets 3 Onyx stars, a Declassified Mission completed on Insane and progress towards beating the campaign on Insane.
Player 2 gets 3 Onyx stars

This may not seem so good but it means that your 2nd playthrough for player 2 only requires that they beat the Declassified Mission on Insane - stars aren't important. This means you can have as many DBNOs (down but not out) during the mission as you like and as long as you live through it you'll get the credit for doing it. Another bonus is that player 2 doesn't have to quit out when you finish the declassified missions on that 2nd playthrough meaning everyone can stay in the game and earn XP.

I credit DarkxMaterials for the solution that told me about the co-op trick in the first place.
I'm taking the credit for figuring out that everyone can get the stars at the same time though

Not to be a downer or hater of the other solution, but I believe in doing things the way they are meant to be played. With that said I am going to give you some advice.

This can easily be done on solo insane and get 3 stars, some missions may take more tries than others but its not too crazy.

TIPS -

Always carry a sawed off shotty and retro lancer when possible. These weapons have the highest damage close range. Especially in levels with large enemies like boomers but especially for enemies like bloodmounts.

Retro lancer or chainsaw execute ragers before they turn! If they turn you can 1 shot their face with a sawed off.

Grenades stick on a regular throw in judgement, if you see a cluster of enemies, stick them and clusterluck those mothers

Markza/Breechshot/ most other weapons refill from normal ammo boxes. Sawed off's, nades, longshots and boomshots do not, refill these with Onyx ammo boxes.

Use turrets and mulchers when available to make quick work of enemies.

Levels with gnasher and ranged turrets, generally you want to place them in the same area and then cover the other side by yourself. If you get in trouble fall back to the turrets and dont forget to reload.

For 3 Stars concentrate on ribbons, executions, headshots, and gibs. Easier ribbons to get involve 5 boltok kills, 3 headshots, 3 executions, and kick tickers before killing them.

Last but not least, have fun and dont expect to pass every level your first try. The AI is pretty good in Judgement so let them do some work if you arent required to do something specific. If you choose to casual glitch this, that is your right to do so, just dont expect any respect from anybody for it.

Game on brothers, enjoy the video below of me beating Karn on Insane with 3 stars :D

Here is a link to a video walkthrough on insane, getting all the stars, and every declassified mission. It has full commentary and should help players of any skill level get these achievements.

http://www.youtube.com/playlist?list=PLTaOHX8kEkD77HyFcClXIm...

Hope it helps.