Cannon Cart is a moving cannon; when its shield breaks, it turns into a stationary cannon right where it stands. It gives value on both offense and defense.
Use Cannon Cart on defense against ground troops; when its shield breaks, it keeps defending as a stationary cannon. On offense it deals high damage if it reaches the tower. It can also support siege decks.
Tips
Remember it turns into a stationary cannon after its shield breaks, and place it accordingly.
Skeleton Army or Mini P.E.K.K.A can finish it quickly.