Cassiopea Guide

Tips for Playing Against Cassiopea

-She can interrupt your W with her W, be careful of that.
-I know this isn't the item section, but swifties is REALLY good vs her.
-Dodging Q denies her poison damage, E damage, and movement speed.
-You could try clicking the laugh button to act like you're about to Q her and then turn around quick to bait an ult
-If you use W to engage while her W is down, I would turn around first so she can't interrupt it with ult.

Swiftness Boots

Swifties allows you to escape her W faster, and more importantly, dodge her Qs. By dodging her Q you don't get poisoned, you don't take extra damage from her E, and she doesn't get movement speed.
Hollow Radiance

Hollow can be a great starting item, as her early game is really good if you end up needing a little bit of magic resist first back. Aside from this, it can be nice to push her into tower.
Heartsteel

Heartsteel is just nice in general. Other MR items might be solid options too though.