Nocturne

If the enemy nocturne is using a life steal build or Mixed with attack speed hes gonna outheal you with auto attacks i usually ban him

Nasus

in endgame he could become a problem if youre ganking top and he has a very high amount of shield

Fizz

Hes a little devil your gonna have a hard time against him when ganking mid

Teemo

also a little devil watch out for mushroom traps especially when hes playing as a jungler

Master Yi

is only a problem in start game because mundo isnt too tanky at the start but end game hes ez

Olaf

while hes uses His R you cant slow him with your q so the best option would be to use your ult without ult he shouldnt be much of a problem

Amumu

Very easy to take care of cuz amumu doesnt do much damage

Rammus

could become a threat in a teamfight but in a 1v1 just use your e and w and auto attack him for a while if hes trying to get away use your q

Sylas

you out tank him most of the only watch out if he copies your R

Hecarim

watch out in early game Because of his high damage and mobility in end game however you out heal/tank him

Gragas

cant do much against you out tank him

Malphite

Hes not a good jungler and even in top lane he hasnt really got a chance against mundo

Zac

Zac is really tanky and has lots of cc and aoe damage but he got no damage but can become a problem in team fights

Jax

Aurelion Sol

Ekko

Karthus

Camille

Elise

Lee Sin