Vayne vs Mordekaiser

Hit the same target three times in a row, with autos or spells: on the third hit, Silver Bolts (W) adds true damage based on their max health.

Slip a Tumble (Q) between two autos: you reposition, and your next attack deals bonus damage. Its cooldown drops from 6 to 2 seconds.

Position yourself so that Condemn (E) pushes your target into a wall: if they hit terrain, they're stunned and take more damage.

Play safe while you're missing your first items: Vayne mostly shines later, when Silver Bolts (W) cuts through big health pools.

During Final Hour (R), each Tumble (Q) makes you invisible for a moment and comes back faster: tumble to reposition while the enemy can't target you.

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.