You're in a team fight, things are going well - then out of the corner you hear "Impure Fools" - and all of a sudden, your team starts dropping like flies. This champion lands a spot on this list because of how exciting she is to watch, and the play making ability that she offers with her mobility, stealth mechanic, and Silver Bolts true damage. The character is labeled as a Night Hunter, her theme dominated by seeking to conquer darkness, basically evil.
Some people have found it difficult in the past to deal with Vayne's amazing dueling capability, which led to LCS caster Phreak replying with "Just 2v1 her.", which became a fairly popular saying on League forums in response to any balance complaints. This girl is the play maker ADC and has always been known as one of the main hyper carries of the bot lane marksman role, and she is one of the front runners of the #LCSBigPlays department. Out of all the champion montages on Youtube - you'll see that the Vayne ones are the most lengthy and considered one of the most interesting to watch, and almost any time a professional ADC locks in Vayne, the crowd goes wild - because when a Vayne is there, you know it's going to be something to watch. When a Vayne goes in for a 1v5, shit goes down.
Tagging some LoL players that might be interested:
At 13, we have Vayne.