Not Updated For Current Season
The masteries shown here are not yet updated for the current season, the guide author needs to set up the new masteries. As such, they will be different than the masteries you see in-game.
Presentation - Vi, the Pitlover Enforcer
To Vi, every problem is just another brick wall to punch through with her gigantic hextech gauntlets. Though she grew up on the wrong side of the law, Vi now uses her criminal know-how to serve Piltover's police force. Vi's brash attitude, abrasive humor, and blatant refusal to follow orders can often infuriate her by-the-books partner, Caitlyn. But even the sheriff of Piltover cannot deny that Vi is an invaluable asset in the fight against crime.
As a child growing up in the lawless outskirts of Piltover, Vi learned to rob and cheat to get by. Stealing and stripping hextech hardware gave her the skills of a master mechanic, while life on the streets taught her self-reliance. When she was six, a ragtag group of criminals took a shine to the young delinquent and brought her into their fold. By the time Vi was eleven, she had become a seasoned accomplice, and she relished the thrill of every heist.
Vi's attitude changed when a raid on a mining facility went bad. She was forced to decide between fleeing with her crew and trying to save the innocent mine workers from a collapsed tunnel. Vi chose to play the hero. While searching for a way to free the mine workers from the rubble, she discovered a damaged robotic mining rig. Improvising, she wrenched off its huge fists and modified them into makeshift hextech gauntlets. Fitting the heavy weapons to her tiny hands, the young girl flexed her arm and threw a powered punch at the rubble. The force of the blow blasted away the rock. With the workers free to escape, Vi fled the scene.
After that job gone wrong, Vi severed her connection to the crew. She returned to a life of solitary crime, but stole only from other criminals. As the years went by, Vi modified and improved her hextech fists, allowing her to bust up heists and snatch loot with ease. Eventually, word of her notoriety reached Caitlyn, the famed Sheriff of Piltover. Rather than seek Vi's arrest, Caitlyn offered the criminal a way to pay her debt to society: work for the law in Piltover. Vi laughed. To her, a job that let her beat up crooks without forcing her to run from the cops sounded perfect. She immediately accepted. Caitlyn now struggles to keep Vi in line, and Vi treats Caitlyn's orders as mere suggestions, but when they work together, they are feared by all lawbreakers in Piltover.
''It's a shame. I've got two fists, but you've only got one face.''
Source : http://euw.leagueoflegends.com/champions/254/vi_the_piltover_enforcer
The Vi [W] "Denting Blows" combined with Black Cleaver and Last Whisper, allows to ignore much of the enemy armor.
If the enemy champion have 100 Armor :
(100 Armor * (8% [Masterie] + 35% [Last Whisper Passive]) - 10.24 [Rune] - 10 [Black Cleaver]
= ((100 * (1-0.43)) - 20.24) = 36.76 Armor.
But we need to add the Black Cleaver Passive and the Vi [W] "Denting Blows", so we have :
((100 * 43% + 25%/5 Auto-attack [Black Cleaver] + 20%/3 Auto-attack [W]) - 20.24) = ((100 * (1-0.88) - 20.24)
= -8.24 Armor
The calculation for each attack is :
(100 * [1-(0.43 + ((25 / 5) / 100) + ((20 / 3) / 100)] - 20.24 = (100 * 0.453) - 20.24
= 25.09 Armor
Conclusion : With this full stuff, Masteries and Runes, each auto-attack ignore 74,91% of the enemy Armor.