The Star.

Spoiler: Tips

The star blocks B's path, but does not block R's.
The ball that is dropped by R needs to be held by B.

Spoiler: Video solution.

Liked the unusual winblock capture.

@ridgerunner Thanks for playing and for the great review. I'm glad you enjoyed this method.

...
so technically,
ball catch the ball ontop of winblock?

@Ray Aznable Hello. Thanks for playing and rating. Technically, I think the ball hits the star. And on the other ball the star blocks B's path..

Yes, the last step was cool ... as always, very nice gameplay & design... thanks @Jóh well done!