People often say "Cassiopeia is a waste of IP, she can't do nothing, her ulti is hard to hit, bla bla".

Those people are horribly wrong.

Cassiopeia is the champion with the most APMs (actions per minute) in the game.
Late game she is popping 600-700 damage every 1,5-2 seconds, just with her Q.

She can harass and chase like mad, deny, scout bushes, scout for stealthed units, jungle, solo lane, gank, get double kill on being tower dived...you get the idea.

These runes are pretty much what you will need: flat cdr and magic pen, so you can make an awesome harass at level 1, and mana regen per 5, so you don't need to get stupid summoner skills like Clarity on her.

Her mana pool will be huge enough, and with golem at level 3-4 it's like child's play.

If you don't want to pick the Doran's Ring at lv 1 then consider getting 3 Quintessences of Fortitude instead.

Masteries are pretty standard for a mage, with improved Ghost, Flash and buff duration (you wan't to have the golem at EVERY TIME!).

This masteries assume you are, like me, a fan of full mobility summoner spells.

Once I was an Ignite and Flash user, and usually went like this.

That improved Ignite really gives a nice AP kick at level 1.

Took Ghost and Flash as I love to go full mobility: facilitates ganking, either using ghost or flashing + ulti through a wall.

Teleport is one of my prefered summoner spells in nukes..so it's pretty viable too.

Ignite, for the reasons I stated above - also, don't forget to swap masteries accordingly.

Exhaust may be useful if they have like 3 AD dps (I'm talking about draft pick here).

Others: just don't, please. You're doing it wrong.

Max Noxious Blast, ASAP!
Follow Twin Fang right away. Cassiopeia is meant to be played Q+E+E+Q+E+E.

Sometimes I don't even put that point in Miasma (only at lv 8 or so).
It DRINKS MANA LIKE HELL and doesn't give that much profit.

Late game is a must though, it's a GREAT zoning tool, so get it, by any means, if they tower hug and won't come from behind him.

Just W behind their minions, parallel to their turret, and don't even auto-attack. Let their minions die. If they start coming to XP range just Q on them: deny has a great psychological impact, making people act impulsively rather than consciently.

True story bros.

Just don't get overconfident.

Ah, point in Petrifying Gaze whenever available.

F*** YEAH! The Items!

Quoting my comment on Cassiopeia:Generic AP Build(up to date) by Th3Em0Sl4yer:

gulag wrote:

Cass isn't mana dependent - never in this life.
She can solo golem at lv 3 and mana issues are gone. That's why 3 Archangel's Staff isn't too good on her.

You want survivability? Damn mate, you're doing it wrong 'cause I don't see anything in the item build. Rod of Ages? Yeah, sure, but for survivability you will also want to get Abyssal Mask and Zhonya's Hourglass.

ALSO something very important on Cassiopeia: you have a lot of AoE, so you might want Rylai's Crystal Scepter too, to slow everyone even more.

This AoE stuff brings me to the last topic: Cassiopeia is a champion that gets LOTS of assists and kills. In a team fight, if you lay your Miasma on the ground, just leave it there and all the enemies die, you get 5 ***its.
With that said, I think Cassiopeia is more than just a candidate for getting Mejai's Soulstealer, it should really be one of her core items.

This covers in fact, almost everything.
His build kinda inspired me to publish this one...as I've seen many, many fail builds in MOBAfire. <- not saying mine is better, just a bit more well thought.

Anyway, this is how it goes:
1- YOU DON'T WANT MID! Don't be silly, where do you get more kills? In a lane with only one guy? Obviously not. Go to bottom or top, with someone with a stun or a taunt ( Rammus, Shen, Sion and Taric are examples of great friends).

G + Click the most squishy, have your lane partner to taunt/stun him, Noxious Blast him to death. Be advised that they usually Flash out...be ready to catch up.

2- Doran's Ring - for your HP and mana regen needs. Also, that bit of AP usually makes a difference in getting first blood.

3- Recall when you have 935 gold and buy Boots, Amplifying Tome and 2x Sight Wards to place in the bushes at the beggining of the river.

4- Build your Amplifying Tome into a Mejai's Soulstealer and grab the Sorcerer's Boots. As I said above, you get a big load of ***its, usually finish with a Kill:Assist ratio of 1...so stack up that Mejai.

5- Time to think: is there anyone that scares the sh*t out of you?
5.1- If not: proceed with Rabadon's Deathcap, starting with the monstruous Abyssal Mask, ofc.

5.2- Yes, and it is AD: get Zhonya's Hourglass. If it's more than one (like, a Nocturne and a Master Yi, you might wan't to get Thornmail <- yes, it makes an HUGE difference when they are dying of your DoT (damage over time), Twin Fang and by attacking you.

5.3- Yes, and it is AP: Abyssal Mask ftw! And it even has an OMGWTF aura that pwns.

Anyway, you are probably getting these 3 items if they have a well balanced team, so the question here is just the order in which you get them <- that also makes an huge difference.

If their team is IMBA (like, full AD or full AP), don't be afraid to stack items like Abyssal Mask or Zhonya's Hourglass.

Once I had Sorcerer's Boots, Rylai's Crystal Scepter and 3x Abyssal Masks against a full AP team and that completely shut them off.

It's all about thinking.

6- If you are feeling OP just sell that Zhonya's Hourglass or Abyssal Mask and get the Void Staff - you will now be facerolling.

I guess that covers everything.

Haven't played Cass lately, so when I do I'll be sure to provide some prints to show that this isn't BS.

If I get the time, maybe also a vid or two.

Any doubts/suggestions will be gladly answered in the meantime.