THIS IS A PENTAKILL BUILD FOR PRO PLAYERS.
Hello Everyone and thanks for Checking out my Cass build. For starters, this build is not for players who cannot land the noxious blast, its like karthas lay waste, it will detonate after a sec from cursor drop point. the idea of this build is that her noxious blast scales pretty well with her AP. So i lane her in Mid if at all possible and its just a bait and pop. u need to watch how the person going against u is playing, is he moving up then using ability then running back. where can u plant your blast to hit him.

PROS:
Tons of damage
slow
harasser
perfect farmer
sexy

CONS:
She is squishy if you are to used to playing tanks this might end up bad.
her ult has its best effect if they look at u and doesnt cast RIGHT away so someone could just turn around and boom, miss on the stone hands but still does lots of damage.

The reason i choose to use these runes is very simple, Her Noxious Blast scales almost 1.0 with her AP. the idea is that, when u land this Noxious Blast on them with a few twin fangs, and they retreat to tower u are most likely in range if u were hitting with twin fang to lane another Noxious blast even if they step into tower range, that last poison could quite possible get u FB very very early on in the match, works for me almost every time.

I use the 9 0 21
Points in offense to get the magic Pen, and the rest in utility for mana regen, Flash, CD and speed. Your Noxious Blast gives you a bonus run speed when you land it. more run speed never hurts when catching up to drop another noxious blast.

MAJOR POINT OF VIEW: By far one of the best masteries ever. Utility Master: increase duration of Neutral buffs by 30%, if ur team helps u get blue at start, or u get it later, doesnt matter blue buff makes you a goddess, u can poison non stop, and faster, and never run out of mana. and to have it last so long, just ruins the other teams chance of competing with her.

First Off, Dorans Ring, HP for survivability, AP to scale with ur poison, and mana regen, nuff said.

on first return grab ur boots. if u can get ur sorc boots. plz do, being able to stay on top of ur enemy is most important. if not get the Tome for AP

next is tricky, If u are flat out dominating ur enemy, face rolling every time u meet. GET THE SNOWBALL ROLLING. Majai is ur best friend at this point. if u are concerned that he is starting to put the hurt on u, DONT BUY IT, Rylais is a must, period but get the belt for HP first it will make a very noticeable difference.

after that point its time to make some choices, are u going to need MR for endgame, or Armor, Zhonias hourglass or Abyssal Scepter. banshee veils for annoying disables

now lets scale that AP like crazy, Rabadons deathcap is a AP wet dream.
Archangels staff really is usefull but if u are playing in right mana should not be a problem with her Passive,(Each ability cast u gain 10% cost reduction to abilities: stacks 5 times)

You have opportunity to be a dream team player. perfect for bad bushes, and lots of AoE damage if u can FOCUS your noxious blast to hits 2-3 people that are sitting on each others laps

LVL1: Noxious blast. Perfect harass and cheap on mana.
LVL2: Noxious blast. Twin Fang. even more harass. (possible time to make some FB)
LVL3: Miasma. Noxious blast. Twin Fang.
KEY KEY KEY KEY. Miasma stacks poison with noxious blast. but its ration is Super low. BUT it slows. So
dont use Miasma if ur low on mana. if u are just returning, person against u is 70% or lower HP. this is when u need it.
OBSERVATION:::::::::::::: Miasma at there retreating side, it has decent range but they will back up if they are any kind of smart. IF u are more then positive this is where they are stepping. NOXIOUS BLAST like simultaneously with Miasma and chase them down with twin fang. OK we are talking a TONNNNN of damage with just that combo. BUT Noxious Blast BOOSTS ur MOVeMENT SPEED!!!! once you twin fang the second time, the poisons are going to wear out and ur Noxious blast has perfect range for 1 more chance to land. U ARE A HARASS CHAMP DoNT LET THEM BREATH.

lvl 6: Petrifying Gaze: This is a very solid ulti. I NEVER SEE PEOPLE WHO PLAY CASS USE IT RIGHT. This is for a sole purpose of stopping enemies who plan on killing u. Dont engage with it!!!!!!!!!!! use ur poisons to work them down. not ur ult. let them think they can kill u, they flash at u, they charge u. ULT them in the face, drop miasma, noxious blast on there heads, and twin fang 4+ times
if they are still alive, u did not build AP items.
BEST TIME TO USE THIS ULT:
let them think they can kill u, they flash at u, they charge u. USE IT
Team fights, Bad bushing, u see the team for 3+ come around the corner walking right into ur bush, ult all 3 in the face Miasma noxious blast and start twin fanging the squishies.
its full proof.

Best someone Spells: that i use
Flash = DO NOT USE TO INITIATEDO NOT USE TO SETUP FOR ULT Flash is probably the best summoner skill on the planet. turning any champ into unpredictable pains. Flash is by far outstanding on Cass, i use it to narrowly escape ganks from jungles, or skill shots that can kill me(ex. Ezreal, lux, Panth, TF ult) or for getting in range to lay that one last Noxious blast. NOTHING FEELS BETTER THEN DROPPING NOXIOUS BLAST OVER A WALL INTO THE FOG OF WAR AND LANDING IT ON SOMEONE AND KILLING THEM.
Ignite = It stacks with ur poisons. COME ON, that is so much freaking damage, if u know its time for them to die, miasma-noxious blast-ignite-twin fang-twin fang- dead

Personally summoner spells are defiantly personal choice, what do YOU use best and if it works for You better, u better do it.