I do have a first idea. Lets see if I can make everything work together as planned:

Background: While digging we found sky crystals that can be used to stop all other movement in the sky. We are a peaceful town. But now the skypirates want the crystals and are attacking us with skydiving pirates. Use the crystals in the beacon to stop time while the invaders come pooring from the sky. We need to gather resources and build defenses to delay the invaders.

Gameplay is divided in two Parts: - On the ground: gather resources and activate the time stopping beacon - In the air on our skyship: fight and build fortifications on the sky islands

I have basic gameplay up and running. The horizontal line is the horizon. Below the horizon is the ground. The unfilled box our skyship which we can enter and fly around in. Beware of the programmer art: