Welcome to my first guide for my favorite champ - Cassiopeia.

Some information about Cassio:
She's an AP-Carry, so in the actual metagame, she's played in the midlane. But, You can also jungle her or play her solo top. I tried out all of these positions and it worked well. Yes, Jungle Cassio is viable. I can tell you: With Cassio, you have to be hyper aggressive so if you normally play defensively, you'll have to learn how to play correctly aggressive without feeding :o If you learn to land your Q/W properly, you will win your lane.

If the enemy team runs double AP Sololane, like Mid Ahri and Top Vlad, I always try to run a double AP-Lane too. Cassio is a good decision for example against Vlad, you hardly counter him.

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Pros + Really strong Harrass + CC + Extremely high Damage Output + AoE Damage

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Cons - Very squishy - Hard to master - Needs shortcast - No natural sustain

For runes, I take:

Marks
9x Greater Mark of Magic Penetration - Standard for Ap Carries, gives you a good amount of Magic Penetration

Seals
9x Greater Seal of Replenishment - I take these runes to make sure I can spam my skills all the day (Also viable: Manareg per lvl; flat AP, Magic resist.)

Glyphs
9x Greater Glyph of Scaling Ability Power - Gives you good extra Dmg over time (Also viable: Magic resist f.e. against LeBlanc)

Quintessences
9x Greater Quintessence of Ability Power - Standard for Ap Carries too, good amount of Dmg.


You can see my Solo Top runes are much different, because you simply can't afford being squishy in Top Lane. I take:
1x Greater Quintessence of Spell Vamp
2x Greater Quintessence of Health
9x Greater Seal of Armor
9x Greater Glyph of Scaling Magic Resist
9x Greater Mark of Magic Penetration

21-0-9 - best choice for most AP Carries with Ignite+Flash

+ - Your best Choice for Midlane

If you go top, I recommend +

Passive: Deadly Cadence
After casting a spell any subsequent spellcasts will cost 10% less Mana for 5 seconds. This ability stacks up to 5 times.
That passive works perfectly with Cassios playstyle.

Q: Noxious Blast
Cassiopeia blasts an area with a delayed high damage poison dealing 75 / 115 / 155 / 195 / 235 (+80% Ability Power) over 3 seconds, granting her 15% / 17.5% / 20% / 22.5% / 25% increased Movement Speed if she hits a champion for 3 seconds.
This is your main Dmg-Skill after your E, max it second. The Movement Speed buff is really helpful to chase enemies. YOU NEED TO LAND THIS SPELL PROPERLY! If you miss it, you can't damage your enemie with your E correctly.

W: Miasma
Cassiopeia releases a growing cloud of poison that last for 7 seconds. Any enemy that passes through it is poisoned for 2 seconds, dealing 25 / 35 / 45 / 55 / 65 (+15% Ability Power) each second and slowing them by 15% / 20% / 25% / 30% / 35 % contious exposure renews this poison.
I only take a point early with lvl 4 and max it last, because I only need this to get vision or to slow enemies when I try to escape. It doesn't do much dmg and the poison lasts only for 2 seconds, the poison form your Q lasts 3 seconds, so it's not that effective in combination with your E.

E: Twin Fang
Cassiopeia deals 50 / 85 / 120 / 155 / 190 (+55% Ability Power) magic damage to her target. If the target is poisoned then Twin Fang's cooldown is reduced to 0.5 seconds.
This is your mainly Damage-Skill. If you land your poison properly, you will just rape your enemy. With a cooldown of 0.5 Secs and if the enemy is poisoned with your Q, you can theoratically land this skillup to 6 times in 3 secs, but you mostly will hit 3-5 of them.

R: Petrifying Gaze
Cassiopeia deals 200/325/450 (+60% Ability Power) magic damage to all enemies in front of her. Enemies facing her are stunned for 2 seconds while enemies facing away are slowed by 60%.
It's an AoE ult which deals TONS of Damage. You can Flash/Engage Teamfights with it, but it's also very useful in 1v1 situations with strong 1v1 champs like Fiddlesticks, you can just ult him when he's using his W or ult.

I usually lvl up Twin Fang first, because this gives you the best amount of dmg, but when your enemy has strong farming abilities (for example Morgana) and my lane gets hardly pushed so that I can't farm, lvl up Noxious Blast first. But I always try to rush my Twin Fang-First-Skillorder.
I lvl up Noxious Blast second because this is your second Dmg-Skill.
At last, I lvl up my Miasma. But I take one point early for the vision and slow.
Take your Petrifying Gaze on 6, 11 and 16 - whenever you can.

The first three levels, you should check if your lane gets hardly pushed by your enemy. So u can find out if you have to lvl up your Noxious Blast first, or if you can go on Twin Fang. Just try not to push but also try to don't let your lane get pushed.
Once you reach lvl 3, you can be hyper aggressive. Harras with your Q and E, simply farm with your Q and try to get first blood, which is very easy on Cassio. Later on, when I have the chance, I'll add some videos where I get easy FB. I don't know much Aps who are strong early, but Cassio definitively is.

-> Take advantage of your range to harrass!

Here is a short video which shows you the early power of Cassio... :D Play Video

Mid Game is where Cassio and most other AP Carries shine. You can be super aggressive and once you have your Rabadon's Deathcap, Phreak would say you deal TONS OF DAMAGE.
In teamfights, try to knock out their AP Carry, if he is not reachable, kill the one who is next to you. It sounds crazy, but you usually can kill everyone 1v1 and in teamfights. With killing the champ who is nearest to you, make it a superfast 4v5. Try to land your ult properly to stun at least 3 people if you're able to. If not, save it, maybe your team has to escape.

-> Posotioning is important unless you want to be focused...

In the End Game, Cassio is not that strong as in Mid/Early game. But, she isn't useless. With Magic Pen, she deals lots of Damage but you can't 1v1 all of the enemy team, Solo Top champs like Garen or Riven simply rape you now and if the AD Carry is fed or if he farmed like crazy, you can't do much. In teamfights, focus squishy targets like their AD Carry (for example Ashe) or their AP Carry (for example Anivia)

-> Don't be that aggressive like in Early/Mid Game!

Let's come to my item build. I don't have the perfect build for all games, because there is none. But, the core build is alwasy the same and should be like this:

And straight rushing

Then you have to decide. If your enemy in Mid get's too tanky and you need tankiness too, get .
If you just need more DMG, get (starting witch )

If you got Rabadon's first, buy now a to get the tankiness you neeed.
If you got Rylai's first, rush .
In your "Rabadons-First-Path", get now a
Then, Magic Penetration would be great. If you need more Magic Resist, get a
If the enemy team is stacking Magic Resist, get .
The last item is your choice. I often get a .
Good viable Choices: (Only get frozen Heart if you got another Build with , which I don't recommend on Cassio)

Much more items are viable on Cassio, I didn't try out that much, just look what you like and maybe write a comment where you talk about your experience with some items.

Going Top always means to not build that squishy as in Midlane, because typical AP-Toplaners are Kennen, Vlad or Rumble. All of these are NOT as squishy as you if built correctly. That means you have to build tanky too, and I think a found a good example build. You also need some early sustain, so make sure that Hextech Revolver is your first core item after Boots.
An example build would be: Mercury's Treads/ Ninja Tabi, Will of the Ancients, Rod of Ages, Zhonya's Hourglass, Abyssal Mask and another Item.

You can choose from these:

More DMG: Rabadon's Deathcap
More HP: Rylai's Crystal Scepter
More HP/MANA/SHIELD: Banshee's Veil
If enemy team has lot of CC: Quicksilver Sash
If you just need more Magic Penetration: Void Staff

You see, Cassio is really strong, but also not that easy to play. I hope I told you some interesting things about her, and if this guide taught you playing Cassiopeia, or gave you at least some useful tips, pls don't forget to like it! If you dislike it, pls tell me why. Have a nice day!