Ezreal vs Varus

Land Mystic Shot (Q) as often as you can: each hit lowers all your cooldowns and adds a Rising Spell Force (passive) stack.

Detonate Essence Flux (W) with a spell rather than an auto: the orb deals its damage either way, but a spell refunds its mana cost plus a bonus.

Save Arcane Shift (E) to escape unless the kill is certain: it's your only way to reposition, on a 26 to 14 second cooldown.

Cast Trueshot Barrage (R) across the map to finish a fleeing target: it hits everything in its line, but deals less to minions and non-epic monsters.

Back off after taking a few autos: each one applies a Blight stack from Blighted Quiver (W), and his spells detonate them for damage based on your max health.

If you can engage, go in while he charges Piercing Arrow (Q): charging slows him, and he has no dash to escape.

Get out of the Hail of Arrows (E) zone fast: the desecrated ground slows you and reduces the healing you receive.

When an ally is caught by Chain of Corruption (R), move away from them fast: the corruption spreads to nearby champions, but dies out if you get far enough in time.