Ninja: The card game of sneak attacks and captures

Description from the publisher:

Ninja is fast paced, fun, and engaging. 2-5 players compete simultaneously to be the top ninja. Choose up to 3 cards from your hand and attack the central Castle. If you have the highest attack, you capture the Castle. Look out for the Castle Guard who blocks attacks. Use the Black Ninja to double your attack. Be the first ninja to 11 Castle points and win!