Gears of War

This achievement speaks for itself - simply kill one hundred enemies with an execution in ranked matches.

An execution kill is when you kill an enemy at close range when they are downed. Approach the enemy, and standing close, shoot their body (or head). You will know if you have performed a successful execution if the icon in the corner of your screen indicates a similar image to that of the achievement picture (seen in the upper left-hand corner of this page.

This achievement is fairly easy to get and just requires you to down an enemy, then either melee hit them or shoot them so get a melee kill. The icon for an execution kill is similar to the achievement image. The achievement can easily be unlocked if you are boosting and if you intend on getting an execution kill everytime then simply shoot an enemy in the legs using the lancer or pistol to down them then shoot them or melee them however but be quick if your not in a boosting session as someone may try and take your kill.
Also, watch out if your playing a match with a quick bleedout time as ifyour enemy bleeds out before you reach them then you cant get a kill or if your on Execution then they may get up again so be quick to finish them off while they're down.

This can be done while suicide-boosting Seriously in War Machine. The player going long will be getting executions.

1) The opposing player going short ("Short") picks up the grenade, then meets up with the long runner ("Long").
2) Long melees Short with the pistol.
3) Short immediately tags Long.
4) Long melees again, downing Short. Stand next to the downed player when the grenade goes off.

Long should get an execution while Short gets a grenade tag kill. This method is a little buggy, especially if the player has a high-latency connection. When I was doing this, about 1/6 of my attempts ended in only my death, while my partner was left bleeding out. This means you may lose a few kills doing this in a match. However, your parter is NOT at risk of losing kills. You may want to set the bleedout time to 5 seconds.

I was able to complete both Curb Appeal and Capital Punishment with this method. This will eliminate the need to use weapons boosting sessions to unlock them.

It's 2020 but Gears boosting is very much still a thing, so here's a more consistent method of getting curb stomps during suicide boosting. With this method you'll get a curb stomp 90+% of the time. The person going for the curb stomp kills needs to be running to the long grenade spawn for this to be efficient and not waste time. You also need to meet infront of the sandbags, so the stomper doesn't accidentally pick up any grenades when mashing cn_X

- Stomper pulls out the snub pistol, shoots tagger once then melees
- Tagger immediately tags
- Stomper mashes cn_X and cn_RT AT THE SAME TIME. What will happen is you'll fire 1 shot, downing the tagger and you'll instantly start the curb stomp animation, Be sure not be face to face as shots will go through sometimes.

The point of this method is that you're damaging the tagger as much as possible without downing them before they tag you, so that after they tag you they only need 1 pistol shot to be downed. The other good thing about this method is that you can get executions the same way. To get executions do the exact same method, but only mash cn_RT after being tagged. The grenade explosion will kill both players, but it will count as an execution for you because you downed the tagger.

Credit to - LordSmorc for helping me figuire this out and testing it multiple ways :)