User blog comment:Willbachbakal/(Champion Rework) Cassiopeia, the Serpent's Embrace/@comment-4888212-20150729020322

tldr: your combo to stack up the poison (which is the main dmg) takes longer without AS, deals less and less reliable damage, and due to taking longer, exposes you to danger longer.

AS stacks the poison faster, achieving maximum free damage faster and allows you to disengage faster, exposing you for a shorter amount to the "danger zone", while dealing maximum damage with maximum safety and maximum reliability and empowering E faster (which deals 2x Qs damage and is point and click)

i wonder what items you would build on her tho. its not worth to stack AP for the 50% AP scaling on her Q.