
Reviewed for patch 7.3d

Favorable matchup
Reviewed for patch 7.3d
Solar Snare's orb and the extra projectiles from Mel's passive travel toward you, and Wind Wall blocks enemy projectiles for 4 seconds. With the root and the poke cut off, Yasuo's melee damage leaves her little to reflect with Rebuttal.
Solar Snare is an orb Mel fires forward that roots whoever is left at its center. Searing Brilliance adds projectiles to her next attack after every ability. A Wind Wall placed between you takes away the root and part of the Overwhelm stacks Mel needs to execute.
Rebuttal reflects enemy projectiles and keeps Mel from taking damage for a moment. Steel Tempest and Sweeping Blade hit up close. What you shouldn't do is release the Steel Tempest whirlwind while the barrier is up: it won't damage her and you'll have spent your engage.
Golden Eclipse strikes every enemy marked with Overwhelm, wherever they are, and deals more damage for each stack. Every projectile the wall stops is one less stack on you, which buys you room when her ultimate is up.
Go in once Mel has spent Rebuttal or Solar Snare. If she still has both, put Wind Wall up before you approach and arrive with the whirlwind charged on minions.
Mel against Yasuo has to bait out the wall before committing her abilities. Throw Radiant Volley at the wave or near him to make him react, and hold Solar Snare until Wind Wall is on cooldown. Rebuttal is your answer to his whirlwind engage; spend it early and you won't have it.

Favorable matchup
Reviewed for patch 7.3d
All of Mel's damage is magic, and Kassadin gains a magic damage shield every time he casts an ability near an enemy champion. Riftwalk takes him to her without firing anything Rebuttal can send back, and Force Pulse finishes the trade up close.
Void Stone gives Kassadin a magic damage shield for a moment every time he casts an ability near a visible enemy champion. Mel's abilities and the extra projectiles on her attacks are all magic damage, so every ability you cast in the trade covers you against part of her answer.
Riftwalk is a blink to a location that deals damage on arrival, not a projectile. It reaches Mel even with Rebuttal ready, and a second Riftwalk in a row deals more damage in exchange for more mana.
Null Sphere is an orb that does travel toward her: if Mel reflects it, part of the damage comes back to you. Throw it once she has spent Rebuttal; if it lands, the 1 second silence stops her from answering with Solar Snare.
Before Riftwalk, Kassadin has no way to reach Mel: farm without stepping up. Once you have it, look for the trade every time she spends Rebuttal or Solar Snare.
On Mel, punish Kassadin before he has Riftwalk: before level 5 he has no way to close in and your abilities reach him from afar. Later on, only cast Solar Snare once he has used the blink, and save Rebuttal for Null Sphere. If he comes in with the shield up, back off instead of emptying your abilities into him.

Execution matters
Reviewed for patch 7.3d
Zed reaches Mel with Living Shadow and Death Mark, and Death Mark makes him untargetable on the way in. It's situational: Razor Shuriken is a projectile Rebuttal can send back and Solar Snare roots him, so it only works once Mel has spent both answers.
Death Mark makes Zed untargetable while he dashes to Mel and marks her; a few seconds later the mark repeats part of the damage you dealt. It's Zed's way in that doesn't depend on throwing anything at her.
Razor Shuriken leaves Zed and his shadows as a projectile. Against Rebuttal you risk Mel sending them back: threaten with Living Shadow so she uses the barrier, and throw the shurikens once it has ended.
Solar Snare roots at the center of the orb and leaves a slowing zone behind. Recasting Living Shadow swaps you with the shadow: use it to leave the orb's path before it arrives, not after.
Go for Mel once she has used Rebuttal or Solar Snare on the wave or on your jungler. With both available, stay at range and farm.
Mel has exactly the two answers Zed needs to avoid, so don't give them away. Save Rebuttal for when the shurikens come, and don't throw Solar Snare at the wave while Zed has Death Mark. When he comes in with his ultimate, aim the orb where he's going to land or at the shadow he can swap back to.