Walkthroughs for custom maps.

The problem here is that when the computer-controlled opponents appear simultaneously, one of the green ones will always run to the corner castles, take them, and destroy our growth.

By the way, you can avoid this problem by having a Rogue with Expert Logistics and Pathfinding skills. I don't remember if you need to give him boots, but with them or without (I don't remember), you can buy up the growth and, using the Rogue, outrun the green opponent in the opposite direction, buying up the growth along the way. And this is only for the case when the green opponent breaks through to the north.
Also, in my playthrough, I leveled up 3 Rogues with elemental skills in the center of the location, and level 10-14 Rogues on the edges of the chain could catch the green opponent with weak/medium forces. Of course, only the main hero could defeat the green opponent with full growth. Sorry for all the spoilers!