Ambushes are great for spicing up your missions.
Just when the player thinks he is home free, and all is well ... then WHAM ... the last think he sees is a horde of scorpion tanks and scudlaunchers!

Basically all you need is a trigger area and a team of enemies. When the player enters the trigger zone then the enemy team is set to hunt or go and defend the triggerarea. Try the map. You need a bit of skill to win.

Try the map, and then take it apart in WorldBuilder to see the scripting.

Get map, zipped