Threats to Vayne with this build
|Yasuo||You can harass it easily.|
Vayne is a short-ranged ADC/ marksman who is arguably the best duelist in the game. Notorious for her incredible late game potential, this hyper-carry deals some of the highest late game DPS in the game thanks to her Silver Bolts. I have played hundreds of games of Vayne in both Solo Queue as well as Ranked Teams. She is my favorite champion and is more difficult than your average Marksman, allowing a high skill cap and room to out-play your opponents.
After Heal received a buff in Patch 4.5 it became a very strong summoner spell in a lot of situations. Defensively, it scales considerably better than Barrier into the late-game. It also provides a 30% movement speed bonus for you and an ally which is effective for both engaging and kiting.
The optimal time to use Heal is against teams with sustained damage and a tanky front-line.
Barrier is a viable summoner spell on any ADC. The shield will help you survive, however with the buffing of both Heal and Exhaust I feel this summoner spell is over-shadowed by other options. If a support does have heal, than barrier can still be an option.
Cleanse was really popular with Vayne early 3rd season. Still not as strong as the heal as of right now. Can be used for heavy CC meta team at bot lane. But your support can just get Mikael's Crucible or you can get Mercurial Scimitar. Cleanse is just not really needed right now.
Flash should be taken 100% of the time on any ADC as it is currently an irreplaceable summoner spell. The increase it provides in both mobility and survivability makes it an essential in any ADC's kit.
ADCs generally limit themselves to one defensive item. The optimal defensive item to build will vary in every game. And it's optional you get two depending on how the game is. The following is a list of the main ones taken by ADCS and the certain situation each of them are best for:
Guardian Angel is a great item against a team which has one set of burst. An example of a good champion to build Guardian Angel against is a Syndra or a Zed who will attempt to full-to-nothing you. Guardian Angel is a strong item as it gives you a second chance, however, if you position poorly you will be killed again as soon as you're revived.
Randuin's Omen is absolutely my favorite right now. Since the Feral Flare started comming out. Most junglers were all about picking attack speed champs and most of the mid laners are now AD. Randuin's Omen stacks great for protecting burst and slowing down enemies that are a little near or on top of you. It also has good advantage on the health where you can easily life steal back up.
Mercurial Scimitar is great against hard CC comps such as Amumu, Leona and Lissandra. Being able to instantly cleanse hard CC means you have have higher DPS and more presence in team fights. However, like the summoner spell Cleanse, it does take skill to put this to good use so make sure you are comfortable with using this item. Keep in mind that knock-ups can't be cleansed, so if their main CC is something like a Malphite, I wouldn't recommend this item.
Banshee's Veil is a safe pick in a lot of situations and provides HP as well as magic resistance. More importantly, however, it provides immunity from long distance initiations such as an Unstoppable Force or a Solar Flare. It is also a good choice if you find yourself against a siege/poke comp as it will be able to block strong poke such as Nidalee's Javelin Toss or Blitzcrank's Rocket Grab and will help to prevent you being pushed off tower.
Playing Vayne (TOP)
Understanding your job as a Marksman /ADC is important. Your job is to deal consistent DPS to the enemy team and your priorities should be as follows:
1) Keeping yourself safe.
2) Attacking Carries and High priority targets, as long as it doesn't compromise your positioning.
A trap for new Marksmen /ADC players is to get too greedy and kill-hungry. Keep yourself well positioned and avoid compromising your safety/position to chase down an enemy unless you have a significant advantage.
In saying that, however, Vayne's kit is better than other Marksmen for assassinating high priority targets and her stealth allows her to repositioning herself in situations other Marksman /ADCs would not be able to survive.