Gain increasing amounts of AD or AP, Adaptive over the course of the game.
Vayne is an AD carry that can have a difficult laning phase because of her low range. Fleet Footwork provides a reliable lane sustain.
The bonus Movement Speed also allows Vayne to reposition and chase targets incredibly effectively.
Triumph here is mainly to keep you healthy after a kill and play up the reset nature of your [R].
Overheal can be another good option here if you think you're going to struggle a bit in the laning phase.
Vayne is all about getting as many auto attack off as possible to proc [W]. Alactrity's bonus Attack Speed also empowers you ability to proc more instances of Fleet Footwork for more healing and chase.
Cut Down is the most reliable form of damage amp for an AD Carry, largely thanks to the fact that you do not build any health items.
Vayne is an AD Carry that relies heavily on proper positioning in teamfights and the extra Movement Speed from Celerity will help to empower your ability to kite.
Vayne is all about late game scaling and there is no better scaling rune than Gathering Storm. If you can make it 30min+ game you will be an unstoppable force in teamfights.