When facing Mundo, pick champions like Rhaast Kayn, Zac, or Aatrox, who have percentage health damage or strong sustain.
Mundo's early game defenses are weak, but he becomes one of the game's toughest tanks with surprisingly high damage in the late game.
Traditional tank Mundo is more effective than "machine gun Mundo"; prioritize tank items like Heartsteel to maximize his late-game presence.