I found very hard to give diagonal motion to the ball, there is some rules to follow in order to achieve a perfect diagonal motion to the ball?
This involved both the x and y axes in the graph editor.
I could tell you the perfect mathematical way to figure it out - but that will be more of a hindrance that help.
The easiest thing to do is build the strength of your 'eye' so you can see where it needs to go.
But here’s a few pointers...
-If the ball is airborne, the horizontal curve will most likely be very linear and even. You will just need to adjust the vertical slope to achieve the diagonal (I’m assuming that the vertical axis is the one affected by gravity)
-If you are trying to achieve a diagonal from the top view (where gravity is not a factor). Then both curves will be linear.
Hope that makes sense.