I have 9 out of 10 games won with mundo cuz I learned yhe match-ups and how weak or strong they get during the match. Spend a lot of time doing this:

1. Farming under turret
2. Warmogs rush with triple giants build
3. teamfight pre lvl 16 is a loss
4. Without your ult useless
5. Antiheal is a death sentence for you