Note- This requires the Catch, Sugar Cookies, Pain Train, Bountiful Harvest, and Emperor Skulls
Take time to build up your forces until you have 2 scarabs and a fully upgraded Arbiter to protect the flag.
Players- 1v1 (Arbiter v Arbiter)
Immediately turn on the Catch, Sugar Cookies, Pain Train, Bountiful Harvest, and Emperor Skulls. Next build 4 warehouses and as soon as you have enough money to do so build a temple, then upgrade your base. Now use your money to upgrade your Arbiter and warehouses. After that you should use the last 2 openings in your base for a shield generator and a summit (Engineers and Banshees). Also, use temple upgrades such as turret strength and population capacity.
While you are doing this your opponent will be building up their base and may occasionally send their Arbiter and some infantry your way, but if you upgrade your Arbiter a bit, you'll be fine.
The first time the flag appears send the ghost you started with to grab it and run to the area ABOVE the middle. DO NOT go back to your base as the enemy will attack you. Don't work too hard trying to get this capture as it is just to buy more time before you start actually going for it. Don't be afraid to let your opponent capture the flag as its first to 3, however don't be afraid to go after them either.
Once you have fully upgraded all warehouses and the Arbiter and purchased a summit and a shield generator, begin to save up money to build a scarab. While this is happening buy 2 turrets. After your first scarab is complete, begin building a second one. Use money you get while this is happening to build 4 banshees and then to fully upgrade your turrets.
You should now have 2 scarabs, a fully upgraded Arbiter, at least 2 fully upgraded turrets, and 4 banshees. Now send your banshees over to the pit above the middle area. As soon as the flag spawns, send your banshee squad to capture it, then immediately fly behind your base (opposite the side facing the enemy base). Now when the enemy comes, simply pulverize them with your forces. Any money made at this time should be used to purchase engineers and more turrets, as well as to upgrade all units that you have. In between flag spawns you should move the banshees back over the pit and heal your units, scarabs are your first priority.