Shape - defines the shape of the bubbles. Possible values are: Bar, Cylinder, Cone, Inverted Cone, Pyramid, Inverted Pyramid, Sphere, Ellipse, Cross, Diagonal Cross, Line Cross, Line Diagonal Cross and Star.

Min Size - controls the size of the bubble with the smallest Size value. 

Max Size - controls the size of the bubble with the largest Size value.

Bubble series always support the Y, Size and Label data point values. If the Combo Chart Subtype is set to XY Scatter, the bubble series will accept a X data point value.