Game Type: Deathmatch
Starting supply and power: 9999
Fog of War: Off
Skulls: You can use player positive skulls if you have them unlocked via finding them in the campaign. (Credit: JVPSHARK)
Everything else should stay the same
Make sure it is 1v1 against a Legendary AI, of course on the opposite team.
I assigned my Legendary opponent to play as Cutter, although it's not necessary for this guide, he's just what I picked.
I played as Shipmaster, again, not necessary, it's totally up to you what character you want to play as.
Step 1: Start the game up.
Step 2: Instantly recycle/destroy your base. (You can rebuild on this base afterward if you choose to do so.)
Step 3a: Because you have 9999 resources, go around and build on every base possible, even the mini bases. This will keep the AI from spreading, locking him in his corner where he belongs. On one of the bases, be sure to keep upgrading the center main base for more unit upgrades.
Step 3b: I recommend building a few Harvesters/Supply Depots/Generators here and there as you wait for everything to build. You can run out of resources if you're not careful!
Step 4: Do what you do best and try to be quick about it. I rushed the AI as hard as I could. Me personally, I built out of the mini base right next door to the AI's base, I spammed grunts and ghosts to keep him busy. I also built an Apex (airfield) on that mini base and built banshees after upgrading a base to Level 2. I built addition units out of the bigger base in front of the AI's spawn to speed up the process and I recommend getting upgrades for your units as well. Don't forget about your leader powers!
Step 5: Amass an army and send all your units to the back of the AI's base and give him everything you got. After the base is destroyed, finish off the remaining units and the achievement is yours.
DO NOT take it slow, RUSH! Keep the pressure on Cutter, if you let him build up, he could come back and win.
See any flaws or have any addition information I should include? Let me know!