Vayne vs Mordekaiser Top Matchup
Vayne Top wins 50.8% of 1,209 Low Elo games against Mordekaiser Top, +2.9 points vs expected, 2-patch window 26.19-26.20.
Researched on LoL patch 26.20. Tips are written to hold at any rank; stats come from Low Elo ranked games up to patch 26.20.
Why Vayne is favored
Vayne's range and Tumble(Q) let her evade Mordekaiser's slow Q/E and kite him with Final Hour(R), including inside his Realm of Death(R). Silver Bolts(W) adds max-health true damage over repeated hits, so Mordekaiser has trouble finishing the duel unless he catches her after Tumble is spent.
How to play as Vayne
Save Tumble(Q) for Obliterate(Q) or Death's Grasp(E), rather than using it to poke. If Mordekaiser casts Realm of Death(R), use Final Hour(R) to kite with invisible rolls and Condemn(E) if he closes the gap.
Mordekaiser's Obliterate(Q) and Death's Grasp(E) are skillshots; Vayne's Tumble(Q) repositions her, and Final Hour(R) makes her invisible during Tumble.
Silver Bolts(W) deals max-health true damage on every third hit, which is effective against Mordekaiser's health-heavy bruiser build.
How to play as Mordekaiser
Do not throw Death's Grasp(E) or Obliterate(Q) while Tumble(Q) is ready; bait the roll first, then use your skillshots when Vayne has less room to dodge.
Sources
These notes come from r/vaynemains and r/MordekaiserMains, checked against the champions' abilities.