You can go Unyielding Pressure against Yago, as you gain extra percentage based damage on your dark siphon (650 when in her travel form, 390 when planted).
Champions with a lot of vertical mobility like Andro or Drogoz can counter her, as she cannot stay in the air for longand her attacks are projectiles, which are difficult to hit to a flying enemy.
It is crucial to avoid her obliteration damage, as she is immune while doing it, deals plenty of damage and will even heal her if she has saved darkness stacks.