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.