Ooh I have a fun ball idea!
A gravity orb - it has no attack damage, but instead pulls other balls towards it and kinda makes a cloud of other balls all following the same path, combining their damage, so if it had a cannonball dealing 50 damage and a plasma ball with 3 power but AOE damage, then the whatever the orb hits is dealt 53 damage in an AOE range, and it keeps going instead of bouncing, combining the effects of what it's absorbed. Or if it absorbs a sniper it can aim itself and break black bricks, etc!