Irelia vs Nasus

Mark your targets with Flawless Duet (E) or Vanguard's Edge (R) before Bladesurge (Q): if the target is Unsteady or dies to it, its cooldown resets.

Before a trade, hit minions with Bladesurge (Q) to stack Ionian Fervor (passive): each stack gives attack speed, and at max stacks your autos hit harder.

Place the two blades of Flawless Duet (E) on either side of your target: only enemies caught between them are stunned.

Use Defiant Dance (W) to absorb a burst: you take less damage while charging, and the longer you hold it, the harder the release hits.

Early on, take a trade whenever he steps up to last-hit a minion: each kill with Siphoning Strike (Q) increases its damage for the whole game.

Freeze the wave near your tower: to farm with Siphoning Strike (Q), he then has to step up and expose himself to ganks.

Once he hits level 6, don't engage during Fury of the Sands (R): for 15 seconds, he gains health and resistances, and his area damage scales with your max health.

In teamfights, if you're ranged, hit him while backing off: he has no dash, only Wither (W), a slow that grows stronger over time.