Perfection of placing and balacing a ball on feet, knee, head while doing 5 balls.
Mastery of “back throw to same side front, other-hand catch”.
3-balls showering, throwing one to the other hand at back.
Blind 3 balls at back
5, 6 balls bounce transitions and to throw/catch
Viktor Kee is one of the best acrobatic 3-ball juggler. What's unusual with Vicktor is that he takes juggling as a dance, acrobatic, art form. As opposed to blunt stunt.
See: Elegance and Respectability of Juggling.