Sounds like **Netstorm: Islands at War**. Played 15 to 18 years ago - it was released in 1997, so entirely possible Took place in the sky - check Collect crystals - check Construct bases - well towers Had mules - the workers were horse/mule type characters Enemies on seperate islands - check Scorpion like enemy - I could see how some of the enemies could resemble a robot scorpion. Build bridges - check That would fall down - they could be taken over, I can't remember if they could be destroyed. Top down view - see below 