This is my guide to Cassiopeia. Since 4 moths ago, she has been my main AP carry and this is just the way I play her and how I came to these conculsions.

Cassiopeia is not an easy champion to play. It requires a good team who know how work with her, she must synergise with her team and coordinate attacks, this is also required without her team as many of her spells compliment each other.

Cass's primary needs are magic damage tools and Movespeed, conting haste and slow.

Defensive stats are always welcome if you are taking alot of hits but it never should be a core focus unless you are building to one specific defensive item.

I play her exclusively with smart cast to speed up casting combos, this is a personal preference but I feel without using this she casts too slow.

( Thanks to Stinglock for grammar and spell corrections).

Greater Mark of Magic Penetrationx9

These runes are standard runes for most of AP carries. It provides you a high amount of magic pen.

Greater Seal of Scaling Mana Regenerationx9

Yellow runes helps you avoiding to run out of mana. They are common in Ap carries too.

Greater Glyph of Magic Penetrationx9




¿Why do I got mark pen blue runes? I know usually AP/level are common runes here and if you let me to say they are better in general AP concepts, for example I use it on my Ap standard page ( Mpen red- Mreg Yellow-Ap/lvl Blue AP flat Q and other variety) but Cassio have good Ap ratios and I start o pick AP from items soon. in my playstyle I will get AP fast in game. Mana regen are just for yellow runes.

Mana regen/lvl are yellow runes: It helps a lot early and they are a nice restoring for whole game.

Quintessences spots are filled with movement speed runes.
Ye, ye, I know that.. now, you will say I rather Ap flat runes mainly. Trust me, I Played with them 3 months and half. Ap flat runes are always good runes for any carry AP in the game, but specificly Cassiopeia needs a good movement to assure your poison spells will not fail.

Masteries are 21/0/9

Masteries in offensive are Archmage' sawy. A little AP is always welcome.
An improved Exhaust, Cripple, since we will got Exhaust most of times.
A little reduction of CDs and finally Archaic knowledge, with this our spells will penetrate a 15% being in a total of 49% with Void Staff and a flat M pen of 13,68 ~14 plus boots ~34.

There is a semifalse known statement what says Mpen don't combine well with Mpen %. The true behind this is the percentatge always applied afterwards will offer an increased ratio of improvement if % Mpen is alone but doesn't mean that the overall penetration will be better.

An exaple for this is if we have 200 X and now we do a 50% minus it will be 100 X but if we have 200 X and we minus 20 so we get 180 and then we minus 50% we will get 90 X. Second Value is lower (100-90) but the flat decreasing was bigger in first one (100-90).

Other Issue is when %Mpen begins to be effective in game, it is good mainly with eemies with high Magic resistance with 120-150 Mres.

For Utility we get Perseverence and 1 point in good hands since we don't use Teleport either Ghost. in tier 2, 1 point in Expanded mind and full of Awareness for increased Exp ratio.
Tier 3, greed and meditation with runes, masteries and a little from items our mana regen will be nice.

Quickness and Blink of an Eye are our tier 4 masteries in Utility. Movement speed is one of more important things at beginning, starting with 333 is a good movement speed early.

Finally we will reduce our CDs a little with Intelligence and our Cds of Summoner spells with Pressence of Master.

In Resume Which will be the key Masteries: Archaic Knowledge, Quickness and our improvements for our Summoner Spells.

First of all, we will get one point inNoxious Blast and it will be the spell we will improve faster, because it is the core spell with one you can begin to do damage, it means evenTwing fang being a better Dps output it is not possible ifNoxious Blastis not hitting, besides this, it gives you an increased movement speed what it means you will hit with fangs more easily.

At level 4 we will getMiasma but it will be the Last skill to upgrade, it gives you a good slow and a good damage to stationary enemies. It helps you a little farming and kiting enemies helped withNoxious Blast.
The other skill isTwing fang, it becomes your burst damage part followed by the decreasing continuous damage. It means spam of this is what gives you burst damage ( Not so high like another AP heros) but it is always with continuous DPS, without this, burst will never exists.

1050 total damage withPetrifying Gaze, no AP, no resistances and being one second inMiasma After 3 seconds. After this you get a 478 DPS ( Without AP). But it requires a good aiming if not your damage will decrease a lot.

Items are just one of more important thing in every game. I have played her in many ways, with Abyssal, with Rylai, starting with Tear of Goddess etc.

But, now I will write the best way I found to build her.

We start withBoots of speed followed bySorcerer's shoes Now we haveSorcerer's shoes next we get 2Dorans's ring Now we haveSorcerer's shoes and 2Doran's Ring. Now we need 1200 gold to getHextech Revolver, you can get this all in once, twice or three steps. Later we will get aWill of the Ancients but not so quickly. BeforeWill of the Ancients, we will build aRabadon's Deathcap will gives us an incredible boost of damage letting you being healed withHextech Revolver. Next step we will finishWill of the Ancients

After this three items the order of next could be a little variated. try to Keep2Doran's Ring with you if you can at all cost. If you see enemies are getting a lot of Magic Resistance or the tank ( With High magic resistance) is being a problem in terms of enemy team damage getVoid Staff, if the game is being ok and you feel good getLich Bane

WithLich Bane you have an autoattacks of 500 approx every 2 seconds, and if you are a good cassio you shouldn't be more than 1 second with no casting in battle, besides of its passive, it offers AP and movement speed, two of keys for this AP carry and a little of Defense vs Magic. ( Specificly I didn't test the benefits of this items until a long time playing with her and now I can say I don't change it for anything).

Last item will be Archmage Staff. With it you will have an incredible mana pool and a good mana regen, anyway this item could be changed for a more deffensive option, if possible try one item with mana or regen mana like anshee's Veil or Frozen Hearth. ( The Deffensive Step could be before lich bane and or Void staff if game is beig bad. If it needs to be your fist or second item play antoher character.

Our Summoner Spells are 2.

Flash: It lets you a lot of things, escape or positioning are the most common things to do, Position is the key of this hero, try always to synergize it will her Ultimate.

Exhaust: It lets you kill and or escape from one enemy.
I played a lot of times with ghost but I consider this spell better for her. Why? Usually, the ranged or melee DPS will try to get you ion the crowd of battle ( tryn, Xin, Yi... Etc) even with ghost you won't be able to escape from them most of times, but with exhaust you will be able to anulate them, even killing them or helping the whole team. This is one of the reasons because frozen heart will be better against physical before Thornmail.

Another good option is Ignite only if Exhaust is covered and they know they need to protect you.

Pros:

Nice Harrass.

Good Aoe Damage.

Good Laner.

Burst/continuous damage equilibrated.

Cons:

Hared to play.

Insults from Kids in Qeues.

Squishy.

Cassiopeia is an underrated AP carry which can carry a game if played well.

In terms of overall damage she is good like another AP.

Frequently we listen that she has no burst but it is not true at all. It have a little, not the best but not the worst, her issue is just to know how to synergize her own spells and to know the damage is being in last seconds more than in first. For example in a ratio of 5 seconds a Veigar/ Annie will do most of damage in second 1-2-3 but Cassiopeia will do in seconds 3-4-5, so many people say, what happen if you die before second 3? No problem damage will be done anyway like if a Veigar dies.

Cassiopeia usually is a mid char. In a typical EU setup Ap carry goes mid, in one of US typical build setups, it depends if you are playing with 2 AP carries or another though like Rumble or Vlad.

The best for Cassiopeia is going mid though she can play in any lane. She can be good playing against 1 or 2 in top lane depending enemies if you know how to farm in your own tower, the worst lane phase is going with AD carry, specially if your lane have not to be pushed because you shouldn't use your zone spells in order to not harrass what mean you will be outfarmed ( more than necessary) by Ad carry wqith autoattacks.

To be continued.

3/1/12: Detailed list of items more accurately and step by step.

* Note: The two doran's ring are not before upgrade boots always. It is optional. First always boots lvl 1 + 3 pots and then Sorc boots or 1 ring, never second doran's before upgrade boots.
It was done in this way in order to not shade sorcerer's boots name.

3/1/12: Changed Archangel'Staff by Rylai.

Both items are good but Archaengel is very expensive if we take account about it is a rechargable item and it is not early game. It provides a good pool of mana, but Rylai synergizes nice with you, even can be more suitable if you get Lich Bane after.