Cassiopeia is, unfortunately, one of the most underrated and underplayed champions Riot's ever released, only really comparable to Karma or Gragas in how few you see. Which is generally none at all. She's also the only character with a maximized Difficulty rating, so doing well with her gives one the satisfaction of competently playing what Riot believes to be the hardest champion in the game.

Of course, if you're reading this, you either already know that feeling and want to experiment with other builds, or you've never really been able to get to that level and want to. Thus is the meaning of a guide, and I'll do my best to cater to both parties by elaborating on my personal build. Keep in mind I've never actually played a ranked game, but I imagine much of what I show will transition to such. Also, remember that if you see something that seems odd in the build summary up top, that I'll be explaining in detail my choices and the logic behind them.

While I'm not going to toggle the comment requirement, I'd appreciate anything I missed being pointed out. And please, read everything through and consider the reasoning I put forth before you decide this build just "won't work". Edit; right, well. Apparently I can't trust people on this, so comment requirement is on, now.

Starting out with a Sapphire Crystal lets you do three things that a Doran's Ring doesn't; it turns into a Catalyst later, it lets you get two potions, and it essentially doubles your mana pool for better harassment, working with Deadly Cadence to more or less let you cast quadruple the spells you would be able to if you had neither. You lose 100HP and 5MP5 5for not taking the ring, but you get to buy a Health Potion that actually gives you 200 Effective HP, and a Mana Potion giving 100 Effective Mana, which more than makes up for it. However, if it seems like you're going to have a hard lane, or you're handling a 2v1, grab the Doran's, since it'll make your life easier overall.

Once you have enough gold for Catalyst the Protector, or Catalyst and your basic boots if you manage first blood, head back and grab it. It's a phenomenal laning tool that'll keep you out farming and harassing practically forever, and the sooner you get it the more effective it is. If you continue doing good, a Rod of Ages is your next trip back's goal. In a recent patch they added Catalyst's functionality to the RoA, so you lose nothing by grabbing it as soon as possible, and it lets you start stacking that passive quicker rather than waiting for Catalyst's usefulness to die off. Plus, it adds a good chunk of AP, and improves the base stats on the Catalyst immensely, even without the stacks.

Your next purchase are your boots. Keep in mind we're eventually getting a Void Staff, so Sorcerer's Boots are not recommended. Instead, you're picking up either Mercury's Treads or Ninja Tabi depending on the enemy team's composition. Yes, you read that right, Ninja Tabi. It ruins the day of AD carries when their attacks have a 12% chance of simply missing. However, if there is more than one hard CC on their team, you're grabbing Mercury's Treads to deal with it. The new Tenacity items are nice, but there's just no room for Moonflair Spellblade or Eleisa's Miracle in the build. Merc treads give you Magic Resist as well as tenacity, so even if there was room, against an AP team you'd be getting them regardless.

Rylai's Crystal Scepter is going to fill in the third slot. It gives a substantial chunk of health, excellent AP, and a 15% slow added to everything you can cast. Yes, even for Twin Fang, since Guinsoo decided a 35% slow that can be applied constantly is bad. What? No, Frost Shot doesn't exist, don't ask. Grab the Giant's Belt first for some immediate health, and work your way up by grabbing the Blasting Wand and then the tome.

Now it's time to start boosting our defenses. Start a Needlessly Large Rod and turn it into a Zhonya's Hourglass for a major AP boost, a good chunk of armour, and the best defensive active in the game. You can use the Zhonya's in many ways, but the most effective are using it to bait someone into standing in Miasma for an extended period of time or recovering from a mistake with Twin Fang, as it'll let you cut the effective cooldown in half.

An Abyssal Mask is next on the list, for the strong AP and the Magic Resist it offers. The aura isn't bad, especially if there are casters on your team who don't have a Void Staff in their build, or if there are no enemies who are specifically stacking MR.

Top the build off with the aforementioned Void Staff. Now, there's a specific note here; the way penetration works is that flat is applied before percentage, meaning if you have any other MrP items, they make the Void Staff less effective. This is why you don't take Sorcerer's Shoes, and why a Haunted Guise, while nice, isn't in the build. Reduction effects aren't as clear cut, and I honestly don't know exactly how it interacts with the Abyssal Scepter, but I can tell you that it stacks multiplicatively with Archaic Knowledge for a total of 49% magic penetration. Of course, if there are absolutely no tanks on their team, and nobody is stacking Magic Resist to counter you, the Void Staff can be exchanged for a Rabaddon's Deathcap just to add a whole new level of pain to your spells. Otherwise though, the MrP % is worth more than some extra AP.

Overall these items will give you a very high amount of health, and solid resistances. Even if the enemy carries get a Void Staff or Last Whisper, you'll still resist a substantial amount of damage. Cassiopeia is like Swain in this respect, while your primary objective is damage, you need to be alive to deal that damage. You don't have Swain's healing, so you need resist gear and health to survive. Of course, you can deal more overall damage than him, so there's a good tradeoff. Even with only 400 AP, you can deal a theoretical maximum of 1165 damage every second, if the enemy is hit by both poisons and you're firing a Twin Fang every half second. Of course, the actual numbers are going to be lower, but you'll still be fully capable of melting faces and surviving.

Masteries are going to be rather standard caster ones. The primary focus is on utilities such as mana regen, cooldown reduction, and experience. I need to stress how bad Perseverance is, though, since a lot of people still choose it. In order for you to gain one single mana per five seconds, you need 25mp5 already. It equates to 4MP5 per 100mp5, and you're never going to have that much, or need that little even if you do. Good Hands, on the other.. hand.. equates to several seconds shaved off your death timer in the event you end up getting killed. It's important late game. Ghost is one of the best summoner spells in the game, and compliments Cassiopeia well because she has no real escape moves; plus, it stacks nicely with the move boost from Noxious Blast. I hate Flash as a concept in general, and use it as infrequently as I can, but on Cass it's extremely useful for charging people and catching them unawares with your ultimate, as well as escaping as, like we just covered, she can't do so on her own very well.

Runes seem odd for a caster, I realize, and I'm going to explain this. I see a lot of people building pure AP pages on Cass, which doesn't really work that well early game, or late for that matter. Think less about yourself for a moment, and about everyone else - every physical carry takes armour penetration marks, and every caster (including you) takes magic penetration marks, the goal being to remove your early game defenses entirely. By taking defensive runes, you compliment the tanking aspect of playing Cass, and adequately protect your laning phase by negating the opponent's penetration. The health quintessences help make her a little tougher early game, and compensate for not taking any of the Doran's items.

I'm not going to claim to have come up with this skilling sequence, because I most certainly did not. Other guides for Cass have it as well, and for excellent reasons which I'll elaborate upon here, once again. Noxious Blast is, at level one, a mana conservation tool. Think about it for a second - all your other spells cost a good chunk of mana at rank one, but Noxious Blast scales down to a simple 15 mana per cast with Deadly Cadence stacked to full. This makes keeping Cadence stacked incredibly cheap, as at level one you'll almost be regenerating that much. It has excellent AP scaling, but the base damage at early ranks isn't that great, so leave it here until mid and late when you have the AP to make it useful.

Twin Fang comes first. It's your main damage spell, and you'll use it to harass people who you've thrown Noxious Blast on while spamming that spell to maintain your passive. It has good base damage and good scaling, so level it up as a priority.

Miasma is second. It deals decent damage without AP, but scales at about 135% if you hit the enemy with all ticks, meaning it's actually your best scaling spell. However, Twin Fang's burst and harassment potential makes it a higher priority. Use Miasma mid game for farming the back wave of caster creeps, and for zoning your enemy.

Petrifying Gaze, obviously, is chosen whenever it's available - at 6, 11, and 16.

Now that you know how to put the points into your spells, and why, it's time to take a good hard look at uses for each of them. Cassiopeia is a very versatile champion, and her spells reflect this; you can use all of them in multiple ways and for various reasons.

First off is Noxious Blast. As I outlined before, early game you'll be casting this practically on cooldown. Note the practically part - Deadly Cadence lasts five seconds, Noxious Blast's CD is three. This means if you wait a second or so before recasting, you'll give yourself time for a bit more mana regeneration. While you're spamming it to maintain Cadence, try hitting low health minions or nearby enemy champions. It's a surprisingly effective way to snag last hits and harass, even with just one point, due to how frequently you cast it. Mid game, once you start picking up some AP, even rank one begins hitting like a truck because of its 90% AP modifier. Late game it transitions into an even stronger ability once you get some more ranks into it, after your mana pool is larger. A nice thing about keeping it intentionally weak and cheap early game is to make your enemies think it's a weak spell, and less likely to avoid it.

Miasma is a superb zoning, farming, and harassment tool. The damage it deals doesn't seem like much at first, but unlike Noxious Blast which shows its duration damage, Miasma shows the DPS. At max rank that'll be 60, +15% of your AP per second. With 400 AP as the build will reach, that gives you about 125 damage per second, over nine seconds. Yes, nine seconds - Miasma continues to poison the target for two seconds after the cloud disperses, meaning that with no cooldown reduction at all you can keep one person poisoned forever; if you manage to snag the golem aura, you can actually keep the entire poison zone up forever. As it has nine ticks, it deals 540 +135% of your total AP per cast, for 1080 damage in an AOE, which is pretty damned decent. Then, on top of that, it gets the 35% slow, which combines multiplicatively with the 15% DOT/AOE slow from Rylai's Crystal Scepter for a 44.75% AOE slow that you can maintain forever. Even if the target leaves the cloud it's still slowed for two seconds. Isn't that nice?

Twin Fang is your nuke. It's your poking spell. It's what makes Cassiopeia viable and dangerous. Imagine the turret on a main battle tank - your poisons are the coaxial machine gun, Twin Fang is the 120MM Cannon. The strange bit is that, as a spell, it's not actually that good; 200 damage with 55% AP scaling on a nuke? Quite bad, in comparison to other nukes. The important part is the cooldown. Now, the tooltip says 0.5 seconds cooldown when you hit a poisoned target, but due to latency and projectile travel time, it's closer to 1, perhaps even 1.5 if your connection isn't great, so don't expect to deal 840DPS with the skill alone following this build, but you'll still pull off very high, very sustainable damage, which only increases the closer you are to the target; shorter range = shorter travel time = shorter cooldown. Compare it to Urgot's Acid Hunter and Noxian Corrosive Charge combo. You need to Smart Cast this spell. Don't feel beholden to casting the spell on a poisoned target though - if Miasma's on cooldown, and you need to slow someone to get away, chase, or save an ally, Twin Fang will proc Rylai's 15% slow, maybe enabling you to get Miasma out. It's also good for last hitting a minion wave affected by a poison. Synergizes better with Miasma than Noxious Blast, since NB's poison isn't entirely reliable for more than one or two Twin Fangs, due to latency.

Petrifying Gaze isn't the greatest ultimate in the game. Even after the last round of bug fixes it's still terribly glitchy, all because of the slow/stun interaction with latency. Maybe you'll target them while they're rushing you, but they're lagging a fair bit and actually turned away before you cast it - since the server checks their position, it'll slow them instead of stunning them, despite you having cast it properly. Of course, if you throw it at their entire team you're probably stunning someone, if not all of them. It deals a good chunk of damage, and scales relatively well, so if you need that extra bit of burst go right ahead and use it on a single target. Even if they're running, the 60% (+6% from Rylai's, for 66%) slow will keep them snared long enough for you to get in range to throw a Miasma ahead of them. Unfortunately, Cass gives a loud gasp and channels for about half a second when casting the spell, so anyone who has excellent reflexes can turn away. 'course, thanks to our Latency friend, they probably won't actually hear it before it's already cast. Lag works both ways.

I'm sure you have, at some point, been completely astounded to be told something that you never noticed but that everyone else takes for granted. Clairvoyance revealing brush when not cast in it is one thing, or knowing that Kayle's Righteous Fury lets her autoattack despite Blinds are excellent examples, but there are dozens more for every aspect of the game. This section will cover a few small things about Cass and her gameplay that might get missed otherwise.

First off, kiting. An often forgotten component of Noxious Blast is the move speed boost when you hit a champion, which combines with Miasma's slow to let you kite enemies to an incredible degree. Cassiopeia is an excellent kiter, and it's a portion of the game that you don't tend to see until higher levels of play; Ashe is better thanks to her permanent 35% slow (I'm not bitter. Really.), but Cass is pretty damned good herself. When you're fleeing, don't just run, retreat in an orderly fashion. Drop poison clouds in front of you so your enemies need to run through them to catch you, and try tagging someone with Noxious Blast so you can speed up for your escape. If all else fails, spin 'round and help them get stoned with Petrifying Gaze; often times that two second stun is long enough for you to start a combo chain and totally reverse the situation, especially given how much damage the spell can do.

On the subject of Noxious Blast's movement increase, there's an intriguing aspect of early game laning that you can take advantage of immediately as you get to your lane. Now, the spell doesn't grant vision of the place it lands, but it'll give you the speed bonus even if the target can't be seen. Phreak pointed this out in the champion spotlight, and it bears repeating given how useful it can be to prevent facechecking brush. Of course, Miasma now grants vision, but it's still more efficient in terms of cooldown and mana to use Noxious Blast for scouting brush. Miasma's more reliable, though, since you get straight up vision, letting you assess a situation more accurately than simply knowing someone is there.

Twin Fang needs to be put on Smart Cast. There's no getting around this, because it's just mechanically faster to hit E than to hit it and then click on someone. Smart Cast essentially means that it'll act like Noxious Blast or Lay Waste, and trigger on whatever is under your cursor. By default it's SHIFT-E, but it's incredibly easy for one's hand to slip - take a moment at the beginning of the game and change the key binding to just E, and switch it back if you play a different champion. This enables you to take full advantage of the miniscule cooldown when you need someone dead right away.

All of Cassiopeia's spells stop her from moving and turn her around to face her target, unlike Irelia's Transcendent Blades which can be fired while running. This means that micromanagement of how your character is positioned is important to minimize the time involved with taking advantage of your opponent giving you an opportunity. You don't want to be turned to the side and telegraph being about to hit them by turning towards them. In fact, you don't want to telegraph your attacks at all, keep them guessing where you're going to poison. While you're spamming Noxious Blast, shift the target area randomly, but hit them every few casts, followed with a Twin Fang, to keep the pressure on.

Miasma is a growing spell. It's one of those entirely unique spells; no other AOE changes its shape or size dynamically, and Miasma has its own unique targeting reticule to show the two different sizes. I fail to see the point, but hey, it lets us abuse the mechanic to confuse people. The trick is intentionally missing with it, so that you'll tag them with the expanding edge, but they don't see themselves standing in it at first, meaning they won't move immediately. Depending on your opponent's lag, attention span, and reaction times, you can sometimes get far more than the two or three seconds they'd normally eat by moving out immediately.

Summoner's Rift, Summer has snakes occurring on the map as untouchable and untargetable critters, just minor parts of the landscape. An interesting thing is that if Cassiopeia is in a game, those snakes aren't. They're removed entirely just for her being present. It offers no gameplay benefit at all, but it's one of those neat things to keep in mind.

In closing, Cassiopeia is extremely effective if you're able to play her properly. She isn't a traditional mage, and building her pure AP will not work. You need to keep in mind that she was meant to be a sustainable DPS champion, not a burst caster. Veigar can handle going high AP to destroy people in a single combo and then GTFO, but Cass needs to stand there and take some abuse in order to wreck face that hard. Fortunately, all of the tank/AP items synergize very nicely with her abilities and playstyle. Like Swain, you aren't a tank, and you should never initiate fights. However, you shouldn't be the last one in either, as you need to keep poisons trained on the enemy team to maximize your effectiveness. Second or third into a fight works just fine, after the tank and bruiser but before the support and ranged. Never underestimate the enemy team, and never overestimate your own.