Ballista + As many cheerleaders as you can place per ballista

Place a certain amount of ballistas (spending ~30-40% of your budget) then equally distribute cheerleaders near ballistas.
First give one cheerleader to every ballista, then give the second one. Keep doing that until you're out of money.

Example of how it should look like:

You can find sercet cheerleader unit on Tribal 1 map on a trunk on the edge of the map near the line divinding sides

Minimum amount of cheerleaders per ballista needed for this combo to have enough power:
3

I usually place 4-5 cheerleaders

Don't rely solely on ballistas, place some melee units near enemies to attract their attention while your ballistas destroy them