Ekko vs Master Yi

Throw Timewinder (Q) at a champion, then position so the device passes through them again on its way back: it expands into a slowing field, and the return hits again.

Hit with Timewinder (Q) out and back, and weave in the empowered auto from Phase Dive (E): the third hit triggers Z-Drive Resonance (passive), with bonus damage and speed.

Cast Parallel Convergence (W) where the fight will happen, then step into the sphere when it appears: you stun the enemies inside and gain a shield.

Engage, deal your damage, then cast Chronobreak (R): you return to where you were 4 seconds earlier, in stasis, and recover health based on what you lost.

Against Highlander (R), don't run alone: regroup with your team, because he gains speed and ignores slows.

If you have CC other than a slow, land it right after Alpha Strike (Q): during the strike, he's untargetable, and Highlander (R) ignores slows.

If you have CC, interrupt Meditate (W): he channels it to heal, more at low health, and to reduce the damage he takes.

Put pressure on his jungle early on: Master Yi is strongest once he has his items, and each stolen camp delays him.