Ekko vs Bel'Veth

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.

Back off when she takes her true form with Endless Banquet (R): she gains health, range and attack speed, and with enough stacks, the form lasts until she dies.

Dodge Above and Below (W): if it hits you, you take a knock-up and her Void Surge (Q) in your direction is refreshed instantly.

If you're the lowest-health enemy near her, get out of Royal Maelstrom (E) range: every slash targets you, and she gains lifesteal and damage reduction.

Deny her large monsters and kills: Death in Lavender (passive) gives her permanent attack speed for each one.