Successfully complete Story mode on the Easy difficulty to unlock Reverse Ball. Alternately, play through half of Story mode on the Normal difficulty.
The Tractor Ball is a bonus downloadable content item. Download it, then successfully complete Story mode again to unlock it in the game.
Successfully complete one of the following tasks to get to the bonus round on the indicated stage:
Stage 1: Get all the orange pellets at the top. A round circle below them will light up. Get the pinball on the circle before the lights disappear.
Stage 2: There are three worm aliens on the left and right side. Knock down all three worms on either side. The door on that side will glow. Hit the door as quickly as possible to open it. The door will now open, and the interior will light up.
Stage 3: Roll the ball around all three blue diamond shaped markings at the top right corner to light it up.
Successfully complete one of the following tasks to get multi-balls on the indicated stage:
Stage 1: There are two sets of worm-like drop targets on the lower board. Get multiple hits to push them all the way in. After all three on the left are done, a gray caterpillar will appear under the top flippers. Hit it once. It will roll up into a ball and become a multi-ball. It will unroll if you lost your original ball.
Stage 2: Hit the ball in the ring in the corner, and get all the yellow pellets.
Stage 3: Kill the snake. The doors it uses to enter and exit the board will become lock shots, allowing up to four balls to be held. Shoot around the right loop on the main board (with the "5000"s) to release them all.