Hi! This is mine first build so i hope you like it ;P!
The world is not always as civilized as people might think. There are still those who would follow the blackest paths of magic and become corrupted by the darker powers that flow through Runeterra. Shauna Vayne knows this fact well. As a young privileged girl in the heart of Demacia's elite, her father tried to convince her of the constabulary's ever-vigilant eye. Young and naive, she truly believed that her world was one of perfect safety, until one night, when a twisted witch took interest in her father. The malevolent woman overcame her father's conciliar guard, then tortured her family before murdering them. The young Shauna escaped only by hiding herself and then fleeing once the hag had departed, plagued by the screams of her loved ones as she ran. A burning hatred was born in her that day, one that could never be denied.

Vayne was able to take care of herself using her father's money, and she began to train as soon as an instructor would have her as a student. By the time she was a fully grown woman, she had become a grim warrior. However, the fields of battle were not to be her home. Demacia needed a protector, one who hunted those lost to the darkness. Shauna used her family's contacts to become the first Night Hunter, and now her prowess is the stuff of legends. It is said that those who practice the black arts quake when they hear that the Night Hunter is on the prowl. Despite her crusade, Shauna has looked at the League of Legends in horror. There are champions who have clearly lost themselves to the blackest of magics, and who have been embraced within the League even though they should be put down for the safety of all. The time has come for the Night Hunter to execute her secret mission - to purge the League of Legends.

Not all shadows are to be feared. At least, if Vayne has her way.



Abilities:

Night Hunter (Passive): Vayne ruthlessly hunts evil-doers. She gains bonus Movement Speed when moving toward nearby enemy champions.

Tumble: Vayne tumbles, maneuvering to carefully place her next shot. She rolls toward the cursor and her next attack deals bonus damage.

Silver Bolts: Vayne tips her bolts with a rare metal, toxic to evil things. The third consecutive attack or ability against the same target deals a percentage of the target's maximum Health as bonus true damage. (Max damage vs. Monsters is capped)

Condemn: Vayne draws a heavy crossbow from her back, and fires a huge bolt at her target, dealing damage and knocking them back. If they collide with terrain, they are impaled, dealing bonus damage and stunning them.

Final Hour (Ultimate): Readying herself for an epic confrontation, Vayne gains increased Attack Damage, stealth during Tumble, and quadruple the bonus Movement Speed from Night Hunter.

Masteries

OFFENSE 21
Brute-force 3/3 , Butcher 1/2 , Alacirty 4/4 , DeadLiness 4/4 , Weapon-expertise 1/1 ,
Lethality 1/1 , Vampirisim 3/3 , Sunder 3/3 , Executioner 1/1


DEFENSE 9
Summoners-resolve 1/1 , Hardiness 3/3 , Resistance 3/3 , Tough skin 2/2


Runes
Greater Quintessence of Desolation 3
Greater Mark of Strength 9
Greater Seal of Alacrity 9
Greater Glyph of Resilience 9

Stupendous Summoner Spells

Flash: Flash is extremely useful for closing the gap on enemies if they're running away, or for jumping over walls to escape from salivating enemies vying for your blood. Flash is a must have on all squishy champions with no escape mechanism. While Vayne has Tumble and Condemn to escape and push back, Flash is a fail safe, as well as being a strong offensive tool.

Exhaust: Exhaust is essential on Vayne to gain the upper hand in any 1v1 fight, or clustered teamfight. Chucking Exhaust on the enemy AD or AP carry immediately shuts them down, and allows you to perform at your full potential. As with Flash, Exhaust can be used offensively, or defensively.

Silver Bolts (W): This ability is very interesting, and what makes Vayne such a beast in team fights/sustained fights. She basically has an in-built sort of The Black Cleaver/ Madred's Bloodrazor in the sense that every third hit (reminiscent of the Black Cleaver) does true percentage damage based on the target's health (reminiscent of Madred's). The BEST thing about Silver Bolts is that it is not affected by Magic Resist.
Tips and Tricks
Silver Bolts won't start crippling enemies until late game, once HP gets higher, therefore it's less of a priority than keeping yourself alive. However, Silver Bolts provide pretty mean burst even on squishies. It gives bonus flat damage in addition to % max health as true damage.
•Never give up in a team fight. The point of Silver Bolts is that it rewards Vayne for continuing a fight. Keep auto-attacking, listen for that audible TWANG and watch in satisfaction as their health is ripped away.
• Silver Bolts makes it very easy to push a lane. Don't auto-attack creeps, just last hit. However, if you are pushing, three hits should take out the ranged minions easily.


Q: Should I Max Silver Bolts first?
The short answer to this question, is "No". The idea behind starting with Tumble first is that you have a low mana cost escape or harrass too. Starting with Silver Bolts is not a great idea due to the fact you won't be auto-attacking at that level.
Silver Bolts is also based off the enemies' health. You have to think of it in a relative sort of way. If they have 100 health, that 4% isn't really going to do anything - ie, you deal 4 extra damage ONLY if you get that 3rd hit. That is what you need to realise. You only do that extra percentage damage, and that base addition when you strike that 3rd hit to proc Silver Bolts. Otherwise, you're just making pretty rings around the object you're attacking.
that it doesn't make much sense, but it does more damage the more amount of health someone has. So ideally you want this maxed out when people start buying health items, not before.
Auto-attack means auto-atacking creeps to push the lane. You don't want to be pushing the lane, because that leaves you susceptable to ganks. In a realistic situation, you will not get that Silver Bolts proc on a laning enemy unless they are ******ed - as you may know, Silver Bolts is only applied to the target for a certain amount of time before it disappears. If you hit them twice, and they pop into brush, unless you're suicidal and follow them, you're not going to get that third hit.
You have to think of health and percent damage as relative.
100 health, 4 damage + 20. (first level)
1000 health, 40 damage + 20. (first level)
100 health, 8 damage + 60. (final level)
1000 health, 80 damage + 60. (final level)
^assuming you get the Silver Bolts proc.
When is it better to get Silver Bolts? When does it do the most damage? When the enemy has more health. You can clearly see that it doesn't do as much damage early game as it would late game. That's what I'm trying to say. The whole point of Tumble is that you Tumble before the third consecutive hit, dealing Tumble + Silver Bolts damage. As such, it's best to max Silver Bolts second or last

Voracious Vayne's Skill Set - Condemn

Condemn (E): This spell is absolutely fantastic. Those familiar with Poppy will find the spell a bit awkward to use, whereas those familiar with Alistar will get the hang of Condemn immediately. It takes a bit of practice to get the best result with Condemn every fight, but you'll get used to it. You should be levelling this out before Silver Bolts if you believe you can land the stuns, otherwise max it out after Silver Bolts.
Tips and Tricks
•Use Condemn to push chasing enemies away from you.
•Try to Condemn enemies into walls. This stuns them.
•Condemn has a large cooldown, despite our cooldown reduction runes and masteries, so don't just spam this ability for the lulz. Use it to save/protect allies/yourself, or to create chaos in a teamfight.

Now, in the below video, I get a kill, and am left on too little health for my liking. I immediately respond to instinct, and Condemn Poppy away from me, so I will be safe. I could have easily cut the part out where I fail with my Condemn, but I leave it in to show that it is a tricky skill to land. Notice that in the space of less than one second, Poppy moves slightly to the left, and I don't move to the left to compensate for this. This error leads to me Condemning Poppy away from myself, instead of into the wall. I could have chosen to chase her, but she still had Flash up, so I assumed she would jump over Dragon wall. Long story short: I fail with a Condemn, I don't chase, and I lose a possible kill. If I get any more negative feedback based upon this video, I'll just simply take it out :)