Small tip for playing against/as Anivia
Against: Her ability slow is actually its own effect called "Chilled" rather than simply being a component of her abilities. If you QSS, Cleanse, or GP W before her E lands it'll remove the effect and it'll do standard damage. Does not work if you're standing inside of her ult and receiving constant ticks of damage that re apply the effect.
As: Ashe R applies the same "Chilled" effect meaning you can proc your empowered E off a targeted that's been affect by either the arrows slow or stun.