Aurora vs Mordekaiser

Poke with Twofold Hex (Q), then recast it once the target has lost health: the hex passes back through them and deals more damage the more health they're missing.

Cast Across the Veil (W) to dodge a skillshot or break a chase: you leap and turn invisible briefly, and a takedown resets its cooldown.

Cast Between Worlds (R) in the middle of grouped enemies: those trying to enter or leave the area are slowed, which keeps them under your team's spells.

Inside Between Worlds (R), teleport from one edge to the other to dodge skillshots and reposition, as long as the area lasts.

Stay near your minions against Obliterate (Q): its damage increases when it hits only one enemy.

Dodge Death's Grasp (E): it pulls you toward him, into his other spells, and it has a 16 to 8 second cooldown.

If you have range, kite him: Mordekaiser has no dash, and only Death's Grasp (E), which pulls you in, closes the distance.

In Realm of Death (R), save your mobility spells to escape him rather than for the duel: he steals part of your stats, and keeps them if he kills you.