Nasus vs Yorick

Last-hit minions with Siphoning Strike (Q): each kill with the spell permanently increases its damage, by more on large minions and champions.

In teamfights, cast Wither (W) on their carry: the slow grows stronger over the spell's duration and also reduces their attack speed.

Cast Fury of the Sands (R) as you enter a teamfight: for 15 seconds, you gain health and resistances, damage nearby enemies, and Siphoning Strike (Q) comes back faster.

Early on, farm rather than force trades: Siphoning Strike (Q) stacks are permanent, and every minion you last-hit makes you stronger later.

Dodge Mourning Mist (E): once marked, you lose armor, his nearby graves keep raising Mist Walkers, and his units rush toward you.

Kill his Mist Walkers, summoned by Shepherd of Souls (passive), before going for him: a single auto or single-target spell is enough for each.

If Dark Procession (W) traps you, hit the wall to break it instead of waiting for it to disappear.

If you can, take down the Maiden of the Mist before Yorick: summoned by Eulogy of the Isles (R), she carries a large part of his damage and push.

Don't let him split push alone: with the Eulogy of the Isles (R) Maiden and his Mist Walkers, he quickly threatens a tower. Send someone to answer him.