Hello!

This probably won't work on a human player, but it definitely works when you are fighting the comp in the campaign. When the AI loses a gold mine, they will obviously try to mine from another source. You can put up guard towers or ranged units (no casters or siege) and they will snipe the peasants/peons as they approach the mine. You want to have enough towers/ranged that the workers will die before they can take a load from the gold mine. Workers are the squishiest units in the game, so this is pretty easy to do. This will shut down their economy, and by extension, their ability to attack your base. It also saves a gold mine for when the one you currently have gets depleted.

Exhibit A: https://imgur.com/a/prjLb0J

Exhibit B: https://imgur.com/a/0jekBpa

That mean you are bad if you need wait till ai will end Gold mine, i suggest attack with more groups, grunts/ogres
dont make trolls, worst unit in w2

The strategy of controlling gold mine is rapidly mentioned here:
http://classic.battle.net/war2/gs/

You can also snipe AI peasants/peons on their way to or from a mine. The AI keeps sending units to their death, you can kill dozens of peasants/peons. This strategy tends to show the limits of playing against the AI :D

Thanks for bringing that up! Ranged is mandatory for the campaign. They probably don't work in multiplayer, but during the campaign the enemy AI makes griffons/dragons. Their mobility means they can cover more areas than towers. The ranger's enhanced damage is a nice touch, and the berserker's regeneration means that you'll end up producing less of them.

I have got World record w2 campaign, trolls/archers are useless, no need to make them vs air, waste of gold

How do you deal with air?

In tod you got air only in 2 last missions, guard but not 30 and mages/dks, i will give you link with speedrun when i will be at home

The screenshots I enclosed were from Beyond the Dark Portal. You fight air most of the expansion.