How to counter Dr. Mundo
Let us take a look on how to beat Dr. Mundo. We will look at champions who are strong against Dr. Mundo and who are weak against Dr. Mundo. Use win rate, gold difference and creep score difference at minute 10 to find the best 
Top champion who counters Dr. Mundo. You can already win in champion select with the right counters for Dr. Mundo. If you want to know how to counter Dr. Mundo then you need to take into account the best picks vs Dr. Mundo and the worst picks vs Dr. Mundo. This Dr. Mundo counter data is based on matches played by Pros on patch 13.21 and previous ones. It is important to see whether Pros counter picked Dr. Mundo or whether they played as Dr. Mundo.
Champions used by Pros to counter pick Dr. Mundo
Looking at the matches from Pros (see table Pros counter picked Dr. Mundo) we can see that they picked 
Jax most often to counter pick Dr. Mundo. The matchup Jax vs Dr. Mundo occured 5 times. Dr. Mundo has 3 wins and 2 losses in this matchup. Learn how to counter pick Jax to get another perspective on the data.
Lane outcome for Dr. Mundo
When looking at Dr. Mundo 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 Dr. Mundo. The lane outcome of Dr. Mundo consists of three outcomes: Win, Loss or Draw. Let's take a look of Dr. Mundo 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 Dr. Mundo.
Conclusion
Analyze the available data and learn how to beat Dr. Mundo. To master Dr. Mundo take also a look on Dr. Mundo builds and runes for Dr. Mundo. Good luck, Summoner!