Caitlyn is a good backup ADC to know, Vayne's a pretty high-risk pick though. As for team comps, it's really up to the team: TSM and CLG usually stick to a very limited choice of champions and develop all sorts of tactics with them (whether they fail or not is another matter). SK and Dignitas may get out of their known picks to counter others...while M5 is just plain unpredictable :P
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