You gain money over time. Use that money to purchase cats to defend your tower and attack the enemy tower. If you have enough money, purchase an upgrade to your worker cat to make more money. When you beat a level or skip it by clicking the shadow in the sky, you get access to a new cat.
Everything from the original game "BATTLE CATS" has been redrawn or repurposed here. GIVE ME CRITIQUE SO I CAN FIX THINGS
