AriisCrystalbane here, despite the contradicting username, that would be summoner name. Been playing as Cass for a bit now, and as she just recently became ftp I decided to make a guide for her. She is a really underplayed champion that can really do a lot for her team with her high AoE damage and her unique utility.

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Other viable options include:

Greater Seal of Replenishment Greater Seal of Armor Greater Seal of Vitality

Greater Glyph of Magic Resist Greater Glyph of Scaling Magic Resist

Greater Quintessence of Health Greater Quintessence of Movement Speed

With the revamp of the masteries, Cassiopeia's masteries have changed drastically going from a 9/0/21 to 21/0/9 or 22/0/8

In offence, grab everything AP, CDR, and Magic Pen related, along with Executioner and Havoc. Putting a point in Wrath if you take one of those spells. And in Utility, grab Expanded Mind as Cass needs a larger mana pool. And the buffed Expanded Mind allows Cass to go a Doran's Ring start for increased damage, survivability, and still retaining her harassing strength.

Starting Items:
+ x3
OR


Core Items:


If you're having trouble surviving:


If you're having trouble sustaining yourself:


If you just need more damage:


If they're stacking Magic Resist:


Typical Endgame Build:


Situational Items:
-Getting heckled by mages or CC? This'll fix it.

-Annoying Suppressions stopping you from doing your job? This'll cure it.

-Lots of AD on the enemy team? This'll keep them off your back. Or dead at your feet, one of the two.

- AS heavy champs after your head? Look them straight in the face and watch them slow down to a halt...courtesy of Petrifying Gaze, of course.

- Getting focused the instant you poke your head around your corner? Freeze time for a moment. That should help.

- Stuck against a bunch of mages that like to have a bit of MR? This'll shut them down AND shut them up. Way to break the laws of physics.

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It's a common item I see built on a lot of casters, for some of them I'd even agree it works. However, for Cassiopeia...it just doesn't make sense.
Her attack range: 550
Noxious Blast: 900
Miasma: 900
Twin Fang: 700
Petrifying Gaze: 700

As you can see. For NONE of her skills do you have to get ANYWHERE close to her attack range. If you want to take a few seconds to get in range and dish out some damage from her auto-attacks you DESERVE to die.

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Passive: Deadly Cadence

(Innate): After casting a spell, any subsequent spellcasts will cost 10% less for 5 seconds. This ability stacks up to 5 times.

This passive is what allows Cassiopeia to spam her skills endlessly with little worry about running out of mana. The 50% reduction at 5 stacks is massive. Without this passive, as a Cassiopeia player you'd find yourself horribly low on mana all the time.

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Q: Noxious Blast

Cassiopeia blasts an area with a delayed high damaging poison, dealing magic damage over 3 seconds and granting her movement speed for 2 seconds if she hits a champion.

Cooldown: 3 seconds
Cost: 35 / 45 / 55 / 65 / 75 Mana
Magic Damage: 75 / 115 / 155 / 195 / 235 (+0.9 per Ability Power)
Movement Speed: 15 / 17.5 / 20 / 22.5 / 25 %

This is Cassiopeia's most powerful skill, it allows her to heckle someone extremely safely as its range is a huge 900. It's not super easy to avoid, they'd have be moving to avoid it. If you hit someone with it you get a massive movespeed buff which would allow you to easily kite, chase, or flee depending on what the situation would require. This skill is also an extremely powerful harassing tool, with its massive 900 range and instant cast time, it can be hard to avoid. If they're always on the move lead them into it, if they're just running sporadically wait until they stop and turn. That is when you use it, more times then not they won't be able to avoid it.

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W: Miasma

Cassiopeia releases a growing cloud of poison that lasts for 7 seconds. Any enemy that passes through it is poisoned for 2 seconds, dealing magic damage each second and slowing them. Continual exposure renews this poison.

Cooldown: 9 seconds
Cost: 70 / 80 / 90 / 100 / 110 Mana
Magic Damage: 25 / 35 / 45 / 55 / 65 (+0.15 per Ability Power)
Slow: 15 / 20 / 25 / 30 / 35 %

This is slightly slower that Noxious Blast, yet just as easy to hit since it's a wider spell. Problem is that it has a higher mana cost and a much lower AP ratio thus making it a terrible choice to use it for damage. But the utility this spell can bring is massive. Throw it ahead of fleeing enemies and they'll be slowed down and less likely to get away. Throw it on top of yourself while you're fleeing and those chasing will end up being slowed.

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E: Twin Fang

Cassiopeia deals magic damage to her target. If the target is poisoned then Twin Fang's cooldown is reduced to .5 seconds.

Cooldown: 5 seconds
Cost: 50 / 60 / 70 / 80 / 90 Mana
Magic Damage: 60 / 95 / 130 / 165 / 200 (+0.45 per Ability Power)

This is where a lot of Cassiopeia's damage comes into play. Target poisoned? Hit them several times with this and just watch their health rapidly deteriorate. It's range is only 700, compared to and which both have 900 range, so I wouldn't use it to harass.

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R: Petrifying Gaze

Cassiopeia deals magic damage to all enemies in front of her. Enemies facing her are stunned for 2 seconds while enemies facing away are slowed.

Cooldown: 120 seconds
Cost: 120 / 160 / 200 Mana
Magic Damage: 150 / 275 / 400 (+0.6 per Ability Power)
Slow: 40 / 50 / 60 %
Stun: 2 Seconds


This is one of your most useful and most difficult to use spells. Sometimes it can be really hard to get the stun off. This is a large reason of why I take Flash. It's an extremely powerful positioning tool and if you + really quickly they more than likely won't be able to react in time giving you the stun.

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With Petrifying Gaze:
+ + + + + +

With this they'll be unable to move so always taking your hits and by the time the stun ends you'll have your miasma on them so they'll have a huge slow on them so they won't be able to escape without either help, or a well placed Flash if yours is currently on cooldown.

Without Petrifying Gaze:
+ + + + +

Starting things off with a slow so they can't easily escape is a better way to ensure the kill, your damage may come later but they won't be able to escape you this time.

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Miasma is a great tool for bush checking, just toss it in a bush and you'll get vision of the bush for a short time. Won't see stealth champs, however.

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Cassiopeia has like no late game. Focus on getting extremely far ahead early game and building tanky (i.e., Rod of Ages, Abyssal Scepter, etc.) enough to survive. She is an amazing harasser and with the advantage she can bring to your team you can get quick and decisive matches as it seems, to them, like they're totally outmatched and have no chance of coming back.

Team fights: Wait for it to start and then flash in for a quick ult causing, hopefully, a five man stun.

Ganking: Like with team fights, you'll be using Flash and Petrifying Gaze for a quick stun, practically ensuring the kill.

Bush Fights: Sit in the front of the bush and when they blindly face check toss Petrifying Gaze if needed.* Quick and easy kill.

*This is something that is based on number of people, which champs are there for both teams, and escape mechanisms including summoner spells they may have.

Please try it out before voting. Any criticism or ways to improve this guide are extremely welcome. Thanks, and please comment.