How do you beat ADC Mordekaiser?
You obviously can't all in him, cause that's kind of his thing. But thanks to his insane healing on W coupled with his everlasting shield, you can't poke him either. If he has a melee support with stun, they'll just instakill you once you leave your turret, if he has a poke champ they'll just poke you down while Morde gives sustain to both himself and support with relic shield and his W heal.
Morde has above 50% winrate against all champions except a few that are rarely played and has played less than 100 games against (small sample size -> inaccurate score) and an average of 56% winrate.