Rek'Sai vs Fiddlesticks

Save Furious Bite (E) for when your Fury bar is full: the bite then deals true damage.

Come out of the ground with Un-burrow (W) under your target: they and nearby enemies take a knock-up, so you can engage or interrupt a channel.

Cast Void Rush (R) on an enemy you damaged in the last few seconds: untargetable, then unstoppable, you lunge at them, and your Un-burrow (W) comes back.

Cast Burrow (W) before crossing the map: your Tremor Sense reveals to your team nearby enemies who move unseen.

Dig with Tunnel (E) near lanes to gank and on your escape routes: each tunnel lasts and can be reused, but an enemy standing on an entrance destroys it.

Stay out of range of Terrify (Q), a targeted spell that reaches 575: if your range is longer, hit him from there without risking the fear.

If you have CC, interrupt Bountiful Harvest (W): he heals during the channel, and if he finishes it, the remaining cooldown drops by 60%.

Spread out from your allies when he arrives: Crowstorm (R) hits every enemy around him, and Bountiful Harvest (W) drains them all.

Ward the brushes and flanks around objectives: spotted in time, he loses the surprise of Crowstorm (R) and the passive fear of Terrify (Q).