Some more ball ideas:
REACTOR: 2 atk 4 hp
Gain 1 attack every 3 times this collides with ANY ball
The bold 1 increases by 1 at every level
THEIF: 3 atk 1 hp
On PLAY, 30% chance to gain Theif Mask
The 30% increases by 30% of missing chance per level up
TROPHY: 2 atk 2 hp
On buy, gain HP equal to the number of wins this lap
RISER: 1 atk 1 hp
On PLAY, gain 1 hp.
HP gains doubles at every level.
SMILE: 4 atk 10 hp
On collide with enemy, gain -2 atk.
The bold -2 increases by one for every level-up