Your Win Condition
Harass him in the early game and get a solid lead pre six Poke him to 65% health and then look to all-in and combo
General Strategy
Try to poke him with Q1s and sometimes Q2 in lane Avoid Q2 Eing forward when you are both healthy and he has his ult or pull up
Trading Patterns
Avoid taking isolated damage from his Q. Being isolated means you take much more damage than if you were in the wave. Hold your E so you can dodge his pull. Spacing him and dodging the pull is everything in the matchup. Mordekaiser has no mobility so you do not need to use your dash to full combo him.
Wave Management
You want the wave on your side so you can freely poke him without him being able to all-in and look for an extended trade with his pull.
Their Win Condition
Survive until six and then look for an all-in in death realm