Added new balls with different playstyles:

Marble — the basic balanced ball.

Plastic — light and responsive, stays on water well, but is affected more by plants and takes more damage from guardians.

Metal — heavy and inert, jumps worse, but is barely slowed down by plants and takes half damage from guardians.

Rubber — bouncy and grippy, rebounds strongly and can also float.

To unlock the next new ball, you need to win with the previous one.