Dr Mundo can farm really easily under his tower. Try to not have the lane pushed against him because it actually benefits him. Instead, keep the wave even or closer to your side of the map so you can receive ganks.
If Dr Mundo is behind, he will start farming with his Q. Do not get in the way of them unless he is trying to secure a Cannon Minion.
Dr Mundo is rather immobile and can easily be killed when locked down. Request assistance from your Jungler to execute him when he is low.
Dr Mundo has lots of sustain thanks to his Passive and the items he picks up. Make sure to invest in Executioner’s Calling or another item that inflects grievous wounds to reduce his healing.
In team fights, Ignite will help reduce his healing, so make sure you Ignite him as soon as he engages.
Crowd control is your best friend against Dr Mundo. If you can layer CC on him in a team fight, it will make it very hard for him to activate his Ultimate R and dish out damage. It will also reduce the healing from his Ultimate R if he activates it if you focus him down and kill him first.
At level 6, Dr Mundo will look to trade more frequently as his Ultimate R provides him with a lot of duelling power and sustain. Keep this in mind whenever he hits level 6.
Dr Mundo can poke you down at level 1 with his Q. Try to dodge as many as possible so you do not have to blow through an early health pot, or become a target for a level 3 gank.
When Dr Mundo has completed Bami’s Cinder, his trading power is much stronger. Do not disrespect his all-in potential once he has this item.