Dr. Mundo vs Malphite Top Matchup
Dr. Mundo Top wins 54.2% of 3,295 Low Elo games against Malphite Top, +4.0 points vs expected, 2-patch window 26.19-26.20.
Researched on LoL patch 26.20. Tips are written to hold at any rank; stats come from Low Elo ranked games up to patch 26.20.
Why Dr. Mundo is favored
Mundo's Infected Bonesaw(Q) deals magic damage based on current health, while his passive blocks the first immobilizing effect such as Malphite's R. That combination lets him absorb Malphite's armor-oriented pressure and denies the reliable engage Malphite usually uses to affect the game.
Measured in High Elo: Dr. Mundo wins 2.8pp more often than expected over 1,215 games.
How to play as Dr. Mundo
Keep your passive available before Malphite commits R, and use Q to chip him without walking into a fight his team can control.
Infected Bonesaw(Q) deals magic damage based on the target's current health, so it cuts through Malphite's armor and can remove his passive shield efficiently.
Goes Where He Pleases(P) blocks an immobilizing effect, which can absorb Unstoppable Force(R)'s knockup if Mundo's passive is ready.
How to play as Malphite
Do not rely on R to stop Mundo while his passive is ready; coordinate another immobilizing effect to pop it first, then look for your engage.
Sources
These notes come from r/malphitemains, checked against the champions' abilities.