Halo Wars 2

Naturally, this is one of the game's more difficult Skirmish-based achievements. It will typically take around 30-40+ minutes to defeat the AI on Legendary; however, there's a very effective method that can ensure your victory over the AI in as little as 6-8 minutes.

To start, head into the Skirmish lobby from the Main Menu and set the map to Sentry. Next, make sure to make these setting changes:

• Gametype: Deathmatch
• Player Defeat on Loss of HQ Timer: 15
• Minibases Count as HQ: OFF
• Starting Supply: 9999
• Starting Power: 9999
• Unit Ability Cooldown: 100%
• Fog of War: OFF
• Leader Powers: OFF
• Skulls: Sugar Cookies & After Party

Now set the AI to Legendary and choose the Shipmaster as their Leader. For the purposes of this method, you'll want to choose the Captain Cuter as your Leader. Once the match begins, follow these steps:

1. Queue up the "Mini-Frag Launcher" upgrade and three Jackrabbits at your main base.
2. Claim every firebase on the map, and the two minibases closest to the AI.
3. Move the Local Rally Point Flag behind the AI's HQ.
4. Queue up the "Support Drone" upgrade at your main base.
5. Build a Supply Pad on the minibase near the AI's HQ and queue up 6 Jackrabbits.
6. Set this minibase's Local Rally Point Flag behind the AI's HQ.
7. Queue up 8-9 Jackrabbits at the minibase in the middle of the map and move its Local Rally Point Flag behind the AI's HQ.
8. Upgrade all of the Supply Pads you've built thus far.
9. Queue up 8-9 Jackrabbit at the secondary HQ you've built in front of the AI's HQ and move its Local Rally Point Flag behind the AI's HQ.
10. Continue to build and upgrade Supply Pads at all of the minibases around the map.
11. Using the three bases of which you've moved their Local Rally Point Flags, continue to produce Jackrabbits.
12. Your Jackrabbits will eventually begin to attack the AI's HQ as they roll towards their Rally Point.
13. After a minute of attacking the AI's HQ, recycle your first HQ and send the Scorpion to join your Jackrabbits (the Scoprion is a product of having the "After Party" skull activated).
14. Claim back your HQ's plot quickly before the AI takes it.
15. Continue to produce Jackrabbits (when possible) whenever your Unit count drops below 80/80.

Once the AI's HQ is destroyed, mop up his remaining Units and the match will end! That's all there is to it. On average, it should only take about 6-8 minutes to defeat the AI if you follow the strategy outlined above.