Halo Wars

This is actually not that difficult, but ridiculously long and boring. It's more a test of patience than anything.

Load up a local 1v1 deathmatch on Release on easy. Do NOT ever turn on a positive buff skull during the match. Play as Sergaent Forge.

The first thing to do is get your first base up and running as quickly as you can and get three spartans out. Use the spartans to clear out the other bases and then contain the covenant in their base. This shouldn't be difficult since the Easy AI is fairly passive. Once all the bases are up and running save the sole covenant base that is being left alone build Grizzly tanks to your unit cap. Split them into two groups. Move one to the flood spawning point outside your base and the other to the flood spawn point outside the covenant base. Park the tanks there for the rest of the game.

Move one spartan up to occupy each release switch, leaving the third with the group outside the covenant base to help out for the rare occasions that the covenant attempt to break out.

What you then do is release the flood spawn points one at a time from the switches, kill the flood and use the repair power on your tanks. It takes I believe 2:30mins for the switches to cool down. Release them again, kill the flood and repair. Rinse and repeat until you have 10k points. I'd recommend watching a movie or TV or something while you do this since it is extremely tedious.

Once you have 10k points turn on all debuff skulls which will give you over a 2x modifier and go kill the covenant. And there you have just as you realize how much of your life you wasted for 15 gamerscore. Don't worry, it didn't occur to me until I was excited I got the achievement and realized I was excited I had sat on my couch for a good chunk of an afternoon bored as hell. Just warning you.

I tried to get this achievement after the update and the Strategic Options Add-on Pack appeared (in case that info matters as the update may have changed things). I followed KOmrades advise, but I stopped getting more points after reaching 4,000 points. Nevertheless, I turned on all the debuff skulls, destroyed the enemy and got the achievement.

Get a Friend to play as any Covenent and get him to keep sending Scarabs after you but make sure you have the "Debuff" skulls for more points and when you get to around 6000-10000 points you attack his base.


Source from Halopedia

Just did this with Scottish Nutter and the game took less than an hour - all the other solutions seem to take longer, so here's what we did!

1v1
Blood Gulch
Standard

The player going for the achievement (Hereafter referred to as Player 1) selects Prophet of Regret, their boosting partner (Player 2) picks Sgt Forge. As soon as the game is loaded Player 1 builds a Temple (to make the Prophet spawn) and surrounds the rest of the base with Warehouses, upgrading to Blessed Warehouses when resources permit, and also upgrades the base and adds extra Blessed Warehouses in the new slots.

Meanwhile, Player 2 is surrounding their base with Supply Pads (as you're playing Sgt Forge, these will automatically be heavy supply pads) - again, upgrade the base and add the extra Supply Pads as soon as resources allow.

Both sides will need plenty of resources to make this solution work, but Player 2 will need more. Rather than waste Resources on building offensive units, though, Player 1 should take the Prophet and clear the 2 rebel bases (using leader power if necessary, Y button for those who don't know) near the middle of the map, letting P2 know when this is done so that P2 can send their Warthog over and claim the Base Locations. P1 should return the Prophet to their base to prevent him shooting P2's 'Hog.

P2 should now create 2 more bases identical to the first, fully upgraded. P1 might want to upgrade the Prophet's Cleansing beam, then once the bases are complete go get a coffee each as you'll need to allow 5-10 mins for resources to build up. Stage 1 is now complete.

Now turn on any debuff skulls you have unlocked. P1 should pick one of P2's Supply Pads and move the Prophet a short distance away. UNLEASH HELL (well, a Cleansing beam anyway!) This should make short work of the Supply Pad, and as soon as it's destroyed P2 should build a Barracks (cheapest building available).

As long as P1 leaves the Prophet's beam running, this will be destroyed almost immediately, before it's even complete. P2 just needs to keep attempting to build Barracks in this spot as the Cleansing Beam fires on it, earning P1 10 points every time a building is destroyed (it's 10 points no matter which building is used, and irrespective of whether construction is complete or not). Doing this will rack up points very quickly. though if either player begins to run short of resources, just stop for about 5 mins and they'll soon build back up.

Given P1 will finish with a Combat Bonus of a 7x multiplier, a score of just under 3k should be sufficient for the achievement to unlock. However, to be on the safe side, I'd continue with this stage until P1's score is around 3,300, then have the Prophet completely wipe out all 3 bases for a further 240 points. If you need to check P1's score during the game, this can be done by pressing the Back button.

This achievement unlocked for me while boosting towards Running the Show achievement. Following guide for boosting Running the Show, I gained 33600 points, which unlocked the achievement. Hope that helps...