Mel vs Gwen

Stay back and poke with Radiant Volley (Q): its projectiles explode in an area up to 950 range, and each hit applies Overwhelm.

Land an auto after each spell: Searing Brilliance (passive) adds three projectiles to it per spell cast, and enough Overwhelm executes the target.

Save Rebuttal (W) for a dangerous projectile: the barrier sends it back to its caster, and you gain a shield and move speed.

Hit your target head-on with Solar Snare (E): only the core of the orb roots, the aura around it just slows and damages.

Cast Golden Eclipse (R) to finish from range: it hits every enemy marked by Overwhelm, wherever they are, harder with each stack.

To hit her during Hallowed Mist (W), walk into the mist or wait for it to fade: from outside, you can't target her.

Take short trades before she lands 4 autos: each one adds a snip to Snip Snip! (Q).

Step out of the Needlework (R) line: she can recast it twice within 6 seconds, with three then five needles.

Answer her split push with two players rather than alone: A Thousand Cuts (passive) heals her on every auto against a champion.