Gears of War 3

Okay—it's time for a real answer. Get this done right the first time around:

PLAY CAMPAIGN—NOT ARCADE or VERSUS. The latter two require "unlocking" executions via multiplayer kills, but there's no such requirement for campaign. I did the following on "NORMAL" and used the Lancer to down the Locust.

ACT 5-5: Ascension

You start with *LANCER*, *GNASHER*, *GORGON PISTOL* (3)—hold down Y over a downed Locust to execute them in style. If you did it right, you'll get a notification in the bottom-right corner. Anya has a *SAWED-OFF* (look at her with LT and press X with your shotgun to trade).

Pick up the *HAMMERBURST*, *BOOMSHOT*, *TORQUE BOW* (3) in the first room (hold down Y). There's a *MORTAR* in the desk area, but you there will be others if you're cramped for time.

After the elevators, there's a *RETRO LANCER* on the right-hand side of the maintenance tunnels. (There's another one later.)

When fighting down the corridor to save someone special, you'll find the *BOOMSHIELD* ("Shield Bash") and a *MULCHER*. Kicking down the doors along the hallway, there's a *RETRO LANCER* on the left and a *ONESHOT* on the right. (4—hold down Y)

ACT 5-6: Reckoning

Make sure you're on at least Normal, otherwise it'll be hard to down the Locust to use the *HAMMER OF DAWN* on them. You can wait for Locust to execute when the Tempest is flailing around (after the cutscene where the Locust grapple up the walls).

There are alternative levels for the Hammer in the comments below.

ACT 2-3: Forced Entry

There's a *LONGSHOT* at the beginning (and a Oneshot if you missed it before). Go ahead and alert the guards. Where the gates open, you'll find *DIGGER*s, a *MORTAR*, and Retros if you missed them before. (3—hold down Y)

ACT 1-6: Hanging by a Thread

You start with a *BOLTOK PISTOL*. Baird has a *SAWED-OFF* if you trade with him (look at him and press X with your shotgun). When the main doors open and the Boomers come out, one will drop a *CLEAVER*. Carry it into the next section for the execution. (3—hold down Y)

ACT 5-2: Blackout

*SCORCHER* is near the beginning (just after the lift stops).

Wasn't that easy? Now let's clean up. Check your Achievements listing in "Stats & Awards" to see what you're missing:

CURB STOMP: Press Y (instead of holding it) near a downed enemy
FACE PUNCH: Hold Y when playing multiplayer/arcade on COG with a weapon that hasn't unlocked special executions yet
ARM RIP: Same, but with Locust
CAPTIVE: Press X to pick up a downed enemy as a meat shield. Press X again to get rid of him.
LANCER CHAINSAW: Hold down B near an enemy with the Lancer (doesn't need to be downed).
RETRO BAYONET: Hold down B and charge into an enemy with the Retro Lancer (doesn't need to be downed).

Find a better location? Let us know in the comments.

Here's a video by TehVGG, if you want (not necessary):

in order to unlock this you must perform every possible execution in the game, this can be done in any more or across any modes (you can do some in campaign, some in multiplayer, and some in horde and it will all count.) also you can check your progress from the stats & rewards from the main menu.

here are the different executions and their respective weapons.
first start off with non-weapon specific executions - then move on to weapons.

i suggest carrying a lancer or hammerburst and shooting the enemies feet to make them crawl so that you can perform your executions.

1. Meatshield-captive (hit x on downed enemy to pick him up as a meatshield and x again to snap neck.)
2.curb stomp (hit y when next to head of downed enemy.
3. face punch ( hold y with standard issue pistol next to downed enemy)
4.arm rip ( i found the only way for this was to play in beast mode using a hold y next to downed survivor)
5. mauler shield-shild bash ( hold y with the shield equipped next to downed enemy.)
6. lancer execution( you need to hold y with the regular lancer for this one.)
7.lancer-chainsaw (this is the chainsaw death, hold b to rev up your chainsaw and cut through enemy.)
8. hammerbusrt(hold y next to downed enemy.)
9. retrolancer (hold y for this one)
10. retro-bayonet( you need to hold b with the retro lancer, this will be a charge type attack- keep charging till you stab a standing enemy)
11. gnasher( hold y next to downed enemy.)
12.sawed-off( hold y next to downed enemy.)
13. boltok pistol( hold y next to downed enemy.)
14. gorgon pistol( hold y next to downed enemy.)
15. torque bow( hold y next to downed enemy.)
16. longshot( hold y next to downed enemy.)
17. boomshot( hold y next to downed enemy.)
18. digger( hold y next to downed enemy.)
19. scorcher( hold y next to downed enemy.)
20. hammer of dawn( hold y next to downed enemy.)
21. one-shot( hold y next to downed enemy.)
22. mortar( this one i had the most trouble with so i went into horde and got 40 kills with the mortar to unlock its execution then held y next to downed enemy. i couldnt get this execution to work until after unlocking.)
23. mulcher( hold y next to downed enemy.)
24.cleaver( hold y next to downed enemy.)

once again the mortar execution was the only one i had to unlock before i could use, whether thats because i did the mortar execution in horde or not im not sure.

I found the easiest way to get this achievement is, select versus and private team death match, put bots and rounds to maximum on casual and put all weapon spawns on the weapon you need the kills and executions on, and a suitable map for the weapon and you will get them in next to no time!
For the Cleaver kills and execution, just go on Horde and within your first couple of waves kill a mauler and pick up the cleaver and it should only take you a couple of rounds to get it! It is also a lot faster to do this by yourself and hog all the kills!

This solution for the Hammer of Dawn execution is EXTREMELY easy to accomplish!

1. Load Versus King of the Hill on Overpass, casual difficulty.
2. Change all weapon spawns to HoD.
3. Use/reload the HoD as needed to get 40 kills.
4. Once acquired, down a Locust w/lancer and perform the execution.

This only took me 15 minutes to complete, could be done faster with friends, the AI tend to get in the way of group kills but I did get several.