Vayne Rework - Keeping Her Core Essence Alive
Foreword
A vast majority of concerns pertaining to Vayne stem from her high damage output and ridiculous repositioning as well as her notoriously inconsistent lane phase. To target these issues, we must first identify what is core to her theme and playstyle, what makes her too much to deal with, and what can be improved in her kit.

Hunter's Instinct (Passive) New
Each time Vayne hits an enemy champion with an Auto-Attack or Ability, she gains a stack of Hunter's Instinct. (Stacks Reset After: 5/8/10 Seconds) For each stack of Hunter's Instinct, Vayne's movement speed is increased by 5/10/15. (Max: 3 Stacks) With the changes proposed for Silver Bolts and Final Hour, I felt Vayne could use a little extra in the ways of dueling. As it stands, Vayne is rewarded only for going forward - but where is the sense in that? This change aims at promoting more strategic trades without allowing her to close the gap too quickly while also keeping her current chase potential at later levels.
Tumble (Q) Re-Balanced
Rolls a short distance. The next basic attack within 6 seconds deals Bonus True Damage that scales with Total Attack Damage (0.45/0.50/0.6/0.65/0.7). With the suggested changes for Silver Bolts, Vayne loses her iconic True Damage. To compensate for this as well as to grant her more consistent poke and trade potential in lane I changed the bonus damage from Physical Damage to True Damage and increased the AD Scaling.
Silver Bolts (W) Re-Balanced
Every third consecutive attack or ability against an enemy deals an additional 30% of Total AD plus 4/5/6/7/8% of the Enemy's Maximum Health as Physical Damage. (Max: 200 damage vs. Monsters)
As it stands, Vayne players stray from more traditional Vayne builds in favor of Attack Speed items (generally Blade of the Ruined King followed by Phantom Dancer or Statikk Shiv). While this is a completely reasonable build path, I also want players to see value in stats such at Attack Damage and Armor Penetration. The former % HP True Damage is a little overbearing and is generally bad for the game where HP is effective against Tue Damage, and Armor is Strong against Physical Damage - Current Silver Bolts bypasses both of these counters. And while the argument that Attack Speed Reduction counters Silver Bolts is perfectly valid, it is actually a counter to Marksmen in general.
Condemn (E)
Fires a bolt that deals 45/80/115/150/185 (+50% Bonus Attack Damage) Physical Damage and knocks the enemy back. Enemies that collide with terrain take 45/80/115/150/185 (+50% Bonus Attack Damage) additional Physical Damage and are stunned for 1.5 seconds.
Final Hour (R) Reworked
Active: Cleanses all Crowd Control Effects. For the next 8/10/12 seconds Vayne gains 25/40/55 Bonus Attack Damage and 15/20/25% Tenacity. The Movement Speed from Hunter's Instinct is also increased by 50% for the duration.
Passive: Upon reaching 3 Stacks of Hunter's Instinct, Vayne's next Tumble stealths her for 1.5 seconds (5/3/1 Second Cooldown). When Final Hour is activated, the Passive is lost until the ability is off cooldown.
Vayne can seem a little squishy at times, especially against teams with Heavy Crowd Control Abilities. To resolve this issue, Activating Final Hour now Cleanses all Crowd Control effects affecting Vayne and grants her Tenacity for the Ability's Duration.
*The stealthing during Tumble was changed to a Passive to always grant Vayne her much-loved potential to outplay. Activating Final Hour disables this Passive until it is off cooldown so as to make using it more timing-reliant. *
These are just Foundations. I am open to suggestions for further buffs and feedback on my proposed changes. I hope my attempt at Reworking Vayne into a worthy AD Carry for S4 is at a more satisfactory level.