Anivia vs Nasus

Recast Flash Frost (Q) when the orb reaches your target: it explodes at once and stuns, without waiting for the end of its range.

Cast Frostbite (E) right after Flash Frost (Q), or inside a fully formed Glacial Storm (R): against a chilled target, its damage doubles.

Place Crystallize (W) behind a fleeing enemy: the ice wall blocks the path before it melts.

Play more aggressively when Rebirth (passive) is available: instead of dying, you turn into an egg, and if it isn't destroyed, you come back at full health.

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.