"All hail the dozen spears of death! Airborne enemies should beware of this sharp, lightning-speed cluster of spears!"
The Sky Tower is a defensive tower that attacks only air units/ flying mercenaries and beast. It shoots multiple times each charge and does splash damage to all mercenaries and beast in the impact zone. This is the most important tower in the game, in the higher levels.
Extra Sky Towers
To be able to build your 3th Sky Tower you will need City Center level 9