Hello Every one My name is ibm181 and i have seen a lot of Cassiopeia builds and i just wanted to throw in my 2 cents. This is my first build and i will try to explain my item, rune, and skill choses as well as i can and why i think they work the best with Cassiopeia. Please provide me with your Opinion and what i can do to improve the build Thanks.

As you can see i picked flash and ignite i find that they fit my play style best and flash is very good combined with Cassiopeia's ult Petrifying Gaze.

Flash - Flash works well as a offensive and Defensive summoner skill allowing you to jump into the fight of run away from a gank. I find that this Summoner skill works with Cassiopeia's Ult very will due to being able to flash in front of people running to hit them with Petrifying Gaze. Using flash has gotten me many kills i would not have been able to get without it.

Ignite - Standard Offensive Summoner skill that most people love i think its great to get first blood but if you don't find it useful you can go with something else like Exhaust.

For Marks i picked a standard mage marks, Greater marks of insight - as every one knows magic pen is key and just helps dominate starting levels especially because she is a DOT champ with her Q and W skills and it works very well with her E.

For Glyphs and Seals i pick Greater marks of Focus - The bonus 48.6 AP that come out of this is just destructive and can mean a big difference with Cassiopeia.

Quints - I use Greater Quints of Force as i stated above Extra AP is nice and Getting a Extra 23.22 more AP from Quints alone power up her skills allot in total thats 71.82 more AP and 8.55 Magic pen at level 18.

Options:
If you find that shes to Squish for you some people use flat health which seams to work if you need it but i don't find any problem with her health same with her mana and for that reason i go Pure AP.

9-0-21 This what i pick for Cassiopeia as i find it works well with her. it is a stranded mage Masteries tree with the exception that i don't get Expanded mind but you can get that if you think it would benefit her more then the extra exp.

I start with a Doran's Ring Every time. I find that it is significant for laining or mid what ever you choose to do i myself prefer laining with a partner.

For my second item, I usually get boots. I usually build towards a Mejai's before finishing my Sorcerer's Shoes. If you are having trouble getting early kills, or are getting ganked, feel free to get the shoes first. As always with Mejai's, if you don't think you can get the kills to justify it, don't bother getting it.

After my Mejai's and shoes are finished, I go after Rylai's next. I love this item on Cassiopeia it just works wonders allowing you to chase down anyone with your speed boast from Noxious Blast. It also gives you the option to go after the belt first if you're feeling squishy, or the AP if you're feeling aggressive.

After the Rylai's is finished, I grab a deathcap to capitalize on the AP I should have from my Mejai's stacks by now.

I then Focus on getting a Abyssal Scepter to get some magic resist for Pesky mages and help out my team with the 20 magic pen from it.

if the game lasts long enough i sell Dorans and get Zhonya's Hourglass and i pick up a Elixir of Brilliance for the bonus 40 AP after words.

Testing items. Feel free to give suggestions.

Noxious blast is an obscenely powerful poke, and you should always get it first. Due to it's low mana cost, it is quite doable to use this as your harass of choice, even at level 1, for the first half of the game, while strengthening your Twin Fangs for committed fights. Obviously, if given the chance, the Q-E harass is best, but even straight Q can work, and often (incorrectly) tricks the enemy into believing you won't be strong if they commit. Bring out the Twin Fangs and profit from their aggression. Also, bear in mind, the speed boost from hitting an enemy champion shows up as a buff on Cassio. You can use this to see if there's a champion hiding in the grass, or even detect stealthers if you have a strong enough sense of where they may be.

Miasma's level 1 slow SUCKS. It will not get people off of you, and really only functions to set up twin fangs, punish a melee on top of you (especially in combination with your ultimate), and to cut off routes of escape. It isn't until it's higher level that it becomes a decent slow, but its damage is still lackluster, since most non-morons will avoid it.

Twin Fangs is your bread and butter. It will destroy early to late game with this build doing over 800 dmg every 0.5 seconds on a poisoned unit late game. This skill allows you to win almost every 1v1 fight around.

Petrifying Gaze is simultaneously one of the most obscenely overpowered ultimates in the game, and one of the most frustrating for the user. When it works right, it is amazing. Wide cone 2 second stun with high damage thats good right? well ya unless they turn away. Your primary use for this is, obviously, for its stun. You can punish people coming at you, either for a gank, or to escape from someone else. During the laning phase, you can also use it, especially while hiding in the grass, to ambush enemies attempting to come for a gank, or jungle, through a surprise stun and quick kill. During team fights, attempt to use it on as many enemies as possible, for obvious reasons. The 60% slow it gives even if you dont attack from the front is decently effective, and can be used to prevent enemies from escaping. I generally wouldn't use it for this purpose unless you're taking down more than 1, or the enemy is an extremely fed carry. If possible, flash in front of them for the stun rather than use the slow.

Over all i find that Cassiopeia can be a hard champion to use but is also one of the best DOT champs around and if you practice like i do you will find that she if very fun to play and can work well with many teams.

I hope you enjoyed the build leave a comment telling me what i can improve as this is my first build i hope to hear from you all soon :D