If you actually read the guide you would know why Twin Fang is maxed last.

Usually when the teams get ready for a teamfight, let's say both teams meet up in mid, but no one initiates..
Having your poison abilities maxed out is a good thing. What I do is to keep harassing them before the teamfight starts. Either they back, because they're all at 50% hp, or they engage, and we have a 100% chance to win. Twin fang is just awesome late game to finish off the easy kills, or even harass the big hp pool guys.

bad guide..why do u max twin fang at the end,this is the best skill for cass,the killer skill...

I had never played Cassiopeia before, but now that she's f2p, I've been trying her out using this build/guide.

Here's the result after a few ranked games:

Thanks a lot!

used a similar build , the morello tome + mp5 runes is pretty solid for mana regen and early game dmg .
Anyway before tf u should grab a blue aura :)

Thanks for the positive feedback, guys! I am going to try to find some time this week to make the guide prettier and include some more info!

I like your guide! Since it's free Cass week, I got to try her out for the first time. Without runes, 23% CDR gives her Q a 2.61 cooldown, so that's roughly about 700 damage with 500 AP. However, I do have to point out that even with her passive, she tends to get mana starved in teamfights. The Rylai's takes care of her health pool, but maybe an Archangel's Staff and/or Rod of Ages (ROA should be mid game, 20 mins, to allow growths) would help with her mana pool.

good i vote up its not bad build and guide

Realy love this guide. I never saw anyone play cassi so i bought her and after playing her i said to myself "well now i know why noone plays her". But after some time i tried her again, with your build/guide and i have to say its rly rly so much more effective. Thank you i find cassi beautifull at last :)

+1
You actually made me want to buy Cass :O
I see so many people fail without a chance when they lvl E first... I am so going to try this. Thanks! :DDD
Edit:
Still haven't tried it yet, but as I am a ginormous fan of Lich Bane and her E and Q have a terribly low cooldown, I suggest you take that into consideration ;)

First guide! Any questions, holler. I'll add more as I think of it.