It's literally the first day of his release, so in all honesty he might not even need adjustment. I'm just bored and came up with some ideas. I tried to be creative and avoid directly nerfing damage tooltips.
1: Remove the Ms bonus on his passive. His core item is Rylais.
2: Increase the amount of hits required to proc his passive. It could be 4 or 5, maybe have it scale down by level.
3: Decrease the duration of his Ult to 5 seconds at rank 1, then have it scale up to 6/7 at 11/16. It isn't even worth putting more then one point into right now.
4: Decrease the speed of his E cast.
5: Decrease the speed of his Q cast.
6: Make his R have a cast time of 1s or something, so the enemy can interrupt it with cc
7: Decrease his auto attack speed.
8: Have his passive cancel or stall while Morde is stunned. Like A-sol stars.
9: Fix Lordekaiser skin.
10: Make it so he can't gain more then one passive stack per 1second.