The rating is 'Medium' -- an average player should be able to win.
I won in 1:05:45 hours. You can watch the game on YouTube or read about it below:
The advantage of 3 players over 1 increases with time. Controlling less than half of the oil derricks leads to defeat. At least one path to the center with its 6 oil fields must stay free of enemies. To that end, distract them so that they do not attack you together until at least one of them is taken out.
Once the game starts, aim to build as many oil derricks as possible -- 16-20 out of 34 in total. Trucks sent to the corners should collect the oil barrels there (6 each) before building derricks. Send Combat Engineers to the centre where they will arrive before enemy trucks. A small army can join, e.g. Grenadiers with Light Cannon Viper Half-tracks. They can kill enemy trucks and fight other units.
In front of your base amass an army. Guard the entries to your base with cannons and place Grenadiers between them. When attacked, ensure all those units join the fight early and face his direction.
Once Hovers are available, send 2 small groups composed of 2 commanders and a truck in opposite directions and on the waterway, where no enemies are expected yet.
Commanders can act as scouts and destroy oil derricks from a safe distance to be seized by the truck. Collect oil barrels in your path. They help to pay an invasion army of ~ 20 Hover tanks. The timer should display around 10 minutes when it is ready.
While an enemy is out of his base, invade it. Prioritise oil derricks, factories and trucks as your foe may soon return. At this crucial moment you must prevent any chance he could rebuild later.
After destroying another base in similar fashion, winning the game shoud be trivial.
The videos show how I won largely due to AI errors and made several mistakes, e.g. not repairing my units or poor scouting.
Surely there are better ways to win -- I am average only.
Thanks to Warzone Atlassian's documentation I could create a challenge file (attached).
Move it under 'challenges' in your profile folder. Due to a bug, version 3.2.1 does not accept it unless you exchange AI descriptions between player 0 and 1.
In "What makes a good challenge" NoQ wrote:
In most of the challenges i tried (or made), the enemy gets weaker over time. Once you are able to survive the early rush and hold your ground for a while, and then manage to control just one more oil derrick, you already won. Simply because you were already equal, and now you have one more derrick, which both makes you stronger and makes your enemy weaker.
This is a simple monotonic curve: you get stronger with every tick, sit there and do nothing but defense (with tanks or towers) most of the time, and then destroy everything in the last 5 minutes.
Most of the challenges around boil down to: survive the early rush, hold your ground for as long as necessary to come up with the winning design (its components may be different), destroy everything with the winning weapon.
This is only partly the case in this challenge which requires good timing and risk-taking. I suggest that it be included in the game by default.