Jarvan IV vs Bel'Veth

Plant Demacian Standard (E), then cast Dragon Strike (Q) toward it: you fly to the flag and knock enemies in your path into the air.

Land an auto as soon as you reach your target: Martial Cadence (passive) adds damage based on their current health, then only triggers on them again after a few seconds.

Cast Cataclysm (R) on a carry who is away from their team: the arena is impassable, and you can recast to collapse it if it gets in your allies' way.

In teamfights, plant Demacian Standard (E) near the allies who are attacking: it gives them attack speed while they stay close to it.

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.