How does Furion's ult bounce?

Solution 1:

Nature's Prophet's ultimate begins bouncing with the nearest visible non-allied unit (it also hits neutrals) to where you targeted. It then bounces to the closest such unit and repeats until there are either no more un-hit units or no more bounces.

Obviously, the later bounces deal extra damage and so you want to manipulate the ultimate so that whatever hero you're trying to gank or lane you're trying to push takes as late of a bounce as possible. This is actually hard to intuitively do: when a teamfight starts that you're in the middle of you're almost always better off casting the ultimate far away from you using the minimap.