GoalSurvive all 20 waves — every invader that reaches the crystal costs you 1 crystal HP.
BuildPick a tower below the map, then tap any lit cell to build it. Path cells are blocked.
UpgradeTap a built tower to select it, then Upgrade (3 levels) or Sell it back for 60% gold.
CombosFrost slows, Cannon splashes, Tesla chains, Sniper snipes. Mix them along the path.
WavesThe next wave comes automatically — call it early with the red button for bonus gold.