Hello,
I would like to create a Pang like game.
Something like this: Pang Longplay (Arcade) [60 FPS] - YouTube
What is the correct approach for you?
The balls should be Sprites or Shape ?
Use physics or bonce extension ?
How to manage the split ball ?
Thanks,
J
Actually physics or using forces or extensions would work just fine
Only difference would be how you gonna setup all crap
As for splitting ball you simply could delete ball that is in contact with spear? or is it hookshot? or harpoon? whatever
Then just create 2 balls where one goes left other goes right
Nothing complicated here you could not find in most tutorials
And since your player would always be at the bottom platform even faking line would be ultra easy
Simply make bullet with that line use bullet extension and make sure bullet is on layer below platform
There would probably be many different adequate way to make that game. But it is a very good idea !
First thing : have you some experience already with Gdevelop ? If not, I would strongly advise you to do one or two simple tutorials. And play a bit with the results (try to modify the games as you wish)
My guts feeling would be to create a different Sprite object for each ball size, and give them a “Physic Engine” behaviour.
For the spear which cuts the ball, I would use a Tiled Sprite. It would allow to make that growing effect.
A bit meta, and probably not what you asked for, but the good approach, is to try things, be curious and tenatious. You can be sure that at first, things won’t work as you wish. But in the end, you will make it 
Here a 10 minutes example