Mordekaiser-2 and 3 shotting people at level 10

I was playing against a morde and he was actually losing lane quite badly. End of game he went 9 and 8 and 8 assists. However around level 10. Maybe 16 minutes the player was 3 shotting people. Literally walking up and melting us with 2 ap items. Literally 2 ap items. At one point he had done to me (Annie with MR shield) him 0 Magic pen. Me with mr of roughly 86 while E is active and being 2 levels above him. He did 1986 damage in 3 seconds. Being 2 levels down and only 2 ap items compared to my 4 items. I couldn't even touch him. I think there's a bug in his damage ramp up. Or a bug in his auto attacks. No ulti just 3 abilities and 1986 damage done. Game happened roughly 9:45 PST ended 10:25 PST Player in question is Kidnapped playing mordekaiser. Server- North American