How to counter Viktor
Let us take a look on how to beat Viktor. We will look at champions who are strong against Viktor and who are weak against Viktor. Use win rate, gold difference and creep score difference at minute 10 to find the best 
Mid champion who counters Viktor. You can already win in champion select with the right counters for Viktor. If you want to know how to counter Viktor then you need to take into account the best picks vs Viktor and the worst picks vs Viktor. This Viktor counter data is based on matches played by Pros on patch 14.9 and previous ones. It is important to see whether Pros counter picked Viktor or whether they played as Viktor.
Champions used by Pros to counter pick Viktor
Looking at the matches from Pros (see table Pros counter picked Viktor) we can see that they picked 
Ahri most often to counter pick Viktor. The matchup Ahri vs Viktor occured 10 times. Viktor has 6 wins and 4 losses in this matchup. Learn how to counter pick Ahri to get another perspective on the data.
Lane outcome for Viktor
When looking at Viktor counters you will notice that win rates alone are not conclusional. Therefore we provide an overview (see table Lane Outcome) where you can see the lane outcome of Pros who played Viktor. The lane outcome of Viktor consists of three outcomes: Win, Loss or Draw. Let's take a look of Viktor lane and match outcome for specific matchups. Considering the lane outcome and the match outcome of a specific matchup, might enable you to find the right counter for Viktor.
Conclusion
Analyze the available data and learn how to beat Viktor. To master Viktor take also a look on Viktor builds and runes for Viktor. Good luck, Summoner!