Castle Defender Saga is a strategy-based arcade game where the player must choose the right heroes and upgrades to protect the castle against an army of monsters. The player can place heroes in the tower and hire lots of archers to defeat the opposing armies. In each round, new enemies will approach the castle. If they get close enough, they will begin to tear down the castle walls. The player can earn EXP and money by defeating the enemies, and use these to level up skills, unlock new heroes, upgrade existing heroes and strengthen the castle.