How to Use King Tower
King Tower is basically unkillable with its high HP. It also quickly takes out pretty much anything in its way. Quickly amassing stars from 2-Elixir units can allow you to build King Tower early.
Playing against King Tower is a nightmare. It blows through shields and draws aggro from your minis. Even if it doesn't destroy you itself, it will distract you long enough for the opposing team to take you out. Your counter options are clear, though. Saint Mirror is a direct counter to King Tower. It's also susceptible to melee swarms and attack speed buffs, such as from Witch, Valkyrie, Lumberjack and Healing Ranger. Of course, racing to own your own King Tower might just be the right call.