Hello, my name is RablyPale, and I'm an average player that plays AP mid. I chose to write a guide on Cassiopeia becasue she is one of the strongest AP champions in the entire game when built correctly. Her skills have extremely high AP ratios and are spammable. She synergizes well when you run her with another AP champion and you both build Will of the Ancients. Petrifying Gaze is perhaps the most powerful skill in the entire game when landed corretly; a 2 second stun on up to 5 people that does 450 damage + 60% of your AP. It happens far too often that I queue into a game and somebody else chooses Cassiopeia and they build her entirely wrong.

I use magic penetration marks because they're pretty much the only marks that are good on any AP carry. There aren't any alternatives.

I use health quintessences because they provies you with a total of 78 more health, which can be the difference between getting a kill and living or not getting a kill and dying in the early levels. You can use AP quintessences if you'd like, but I find the health nicer for laning, especially since your damage is already really high. another option are magic resist if you're going against something that does a lot of burst damage (Like leblanc), or a combination of magic resist and health.

I use mana regen per 5 seals because if you're going to ahve any mana problems, it will be early game. Usually your jungler should be giving you the second blue buff so you can spam even more, but with these and 2 Doran's Rings, you can maintain a decent level of mana even without it. If you know they're sending something like Talon or Pantheon mid to counter you, you can run armor instead. I wouldn't reccomend mana regen/lvl, but they work.

For glyphs, I use magic resist. If you don't run magic resist glyphs when you're mid lane, you will take a lot of damage from the opponent and may even lose trades. You can take AP/lvl glyphs if you'd like, but magic resist is much better.

I usually go the standard AP carry masteries, 21/0/9. I take improved recall instead of swiftness because the 0.5% move speed really isn't that much. Also, your Noxious Blast gives you move speed when you hit a champion with it.

Another possibility is to go 21/9/0. Put 3 into resistance and 1 into hardiness ( or 2 into each) and then go for Veteran's Scars. This makes you tankier which allows you to be more aggressive and win more trades. The downside to this is you end up with less mana regen and a shorter time with blue buff.

Core items

This is the standard opening on most AP mids. Often times I see people start with Doran's Ring, and this basically immedately means you win the lane. You start boots becasue most AP carries have at least 1 spell that is skill shot reliant, and it is a large portion of their damage. Boots give you an easier time dodging that skill shot and the health potions give you sustain. The person that started Doran's Ring has a more difficult time landing your skillshot and has less sustain (this applies for any AP carry, not just Cassiopeia).

sight ward It's a good idea to buy some Doran's Rings, just not as a starting item. They provide you with more health and some damage and even some mana regen. This lets you stay in lane for even longer. The health potion is to let you stay survive in lane since you don't have Hextech Revolver yet. The ward should be place near your wraith camp to prevent some counter jungling and so you can see incoming ganks.

Your next purchases are to increase your damage and sustainability. At this point, if you land a Noxious Blast and 2 Twin Fangs, you should be doing ridiculous damage.

This is an important item to get as it increases your survivavility in teamfights.

This item is amazing. It gives you a total of 80 AP 20% spell vamp and provides your teammates with 30 AP and 20% spell vamp. When you have a Rumble or other AP champion top lane and you both have this item, your teamfights become significantly stronger. You can also sustain in lane better and deal more damage because of the AP.

This item synergizes very well with your Q. When you hit a champion, it slows them, and your Noxious Blast speeds you up. This allows you to land your Noxious Blast again and hit them with Twin Fang several times.

30% more AP yes please.

Items to consider

For the last 2 slots, there are many options. I usually build Void Staff for one of them and a defensive item as the other.

This item is amazing. If the enemy team has even one or two peopel with over 100 magic resist, get this. You can get it before finishing Rabadons or Rylai's if they're really tanky and you don't do damage.

This is usually my choice after Void Staff. IUt provides you a little bit of survivability agains ttheir AD carry and it allows you to take some damage, cast Noxious Blast and Miasma and then use it's active effect to regen yourself to full health. It can also be used when they're focusing you, so they have to immediatley switch targets or they lose 2 crucial seconds of a fight.

This item is a bit unorthodox, but after watching Ocelot play and seeing him build this and Will of the Ancients, I realize how awesome it is. In lane, it increases your sustain (increased healing + magic resist). In team fights, it increases survivability and damage output (health+cdr).

These boots are a good choice sometimes. Instead of building Sorcerer's Shoes agaisnt a lane like Veigar or a team with lots of crowd control becasue of the tenacity.

I'll usually rush this item after Hextech Revolver against a lane and jungler with lots of crowd control (Malzahar or Veigar + Rammus is a definite must).

This item isn't usually the best choice, but if you feel like their AP carry is doing too much damage to you but they aren't using crowd control on you, this is decent. It's also pretty good when you're running double WotA.

Another unorthodox item, if I opt to go for this I'll build it out of the Giant's Belt that I would usually build my Rylai's Crystal Scepter out of. It works wonders when their AP carry is killing you immediately in fights (the best way to counter burst damage is with health).

This item is okay when you don't need defense. I still recommend a defensive item anyway.

Items some people get that I don't reccommend

Itemizing Cassiopeia is where I see many players go wrong. Sometimes I see people build things that they think work well on her, and sometimes the items do, but there are so many better options. These items all work on her, but other items offer much better utility.

I see a lot of people build Tear of the Goddess as their first item thinking it is a good choice. I don't think it's that great, mainly because there are so many better options available. It also takes a long time for it to be worth it, and the price is high for what it does.

This item isn't the worst thing possible, but I don't really like it. It sets back your Hextech Revolver too much. For the 3035 gold it costs, you can get your 2 Doran's Rings, Hextech Revolver, and Sorcerer's Shoes.

Even though this item gives the most AP in the game for a very low price when it has full stacks, I find there are items that give more stats and are better fit for an item slot.

This is your passive skill. Most people underestimate it and think it's useless, but it's actually amazing. Instead of Twin Fang casting 90 mana, it costs 45 mana. It lets you spam and keeps your mana at a decent value thrught early game.

This spell is the skill you're going to max first. It deals a bunch fo damage with the 0.8 AP ratio. It has a very low cooldown and can be used to clear waves very quickly.

This skill has a reall small AP ratio, but it is still quite useful. It covers a small area that increases in size over a period of 7 seconds and applies a slow on anyone standing in it and for 2 seconds after they leave it. You will only get 1 point in this spell until level 14. You can rank it up at either level 2, 3, or 4, depending on the enemy jungler and if you think you'll get a kill if you rank it. Usually if the enemy jungler is a Rammus, I will get it at level 2 in case he ganks becasuse the slow can stop him from reaching you if placed properly.

This skill is your primary source of damage after inflicting a person with poison. It regularly has a 5 second cooldown, but if you hit a person that is poisoined with it the cooldown decreases to 0.5 seconds. This makes you a master at trading in lane and makes your damage output in teamfights extremely high.
I recommend always smart casting everything on evert champion, but if there was 1 spell I wish everyone smartcasted, it would be this spell. It reduces the delay between casts and increases your damage by a large amount.

A double edged sword (to some extent; at least for the stun/slow part), and perhaps the most powerful and useful ult in the game. It is extremely difficult to land the stun on all five opponents, but if you succeed, your team should win the fight. At max rank, it is a 2 second stun or 60% slow plus 450 + 60% of your AP in damage. Usually you will only be able to hit 3 people with it, but it is still very powerful. You can turn a game around if you land it properly, even if you're 15k gold behind.

I take this spell most of the time. It adds to your already high potential to get kills.

There are times that you can Flash + Petrifying Gaze and get three or four people with your stun. It can also ensure kills in laning phase and can help you escape ganks.

Any time I see the enemy team has Rammus, I immediately replace Ignite with this spell. Basically when a tema has strong crowd control or a jungler that can pull off ridiculous ganks, Cleanse is a good choice.

I don't recommend any summoner spells other than those three because nothing else offers very much to your team except perhaps Exhaust

As on all champions, farming on Cassiopeia is very important. It is also important to try to deny your opponent of creeps by zoning them with your Noxious Blast Twin Fang combo. If you notice your opponent goign in for a last hit, you should be able to predict where they will go and Noxious Blast them and hopefully land a Twin Fang. Eventually, they will have to choose between last hitting or not beign able to get gold because of how high your harrass is. When you ahve Hextech Revolver, you can use Noxious Blast and Miasma to push your lane and either:

Gank top lane
Gank bot lane
Take your jungler's wraiths if he isn't clearing them
Take the enemy jungler's wraiths (I recommend warding somewhere near them to make sure you're safe)

Cassiopeia is very good at clearing Dragon and Baron quickly. Once you get a good gank on your opponent's bottom or mid lane or oyu see their jungler top, you, your bottom lane, and jungler can usually do Dragon. It's usually a better idea to make sure the enemy bottom lane is pushed out of lane first and to make sure their jungler can't steal it.

Baron, on the other hand, can be done at around 20 minutes as long as you have blue buff and someone to tank it for you or you have somebody else on the team with Will of the Ancients (Rumble is probably the best for this) and your jungler. Just ask your jungler to grab a Vision Ward or Oracle's Elixir (it's usually a good idea for the jungler to have an Oracle's Elixir by this time anyway) and have him check baron for wards. If it's unwarded, the three of you can clear baron quickly enough that the enemy probably won't notice. If it is warded, the jungler should remove the ward and then wait 15-30 seconds to see if they try to reward (if they do, it's probably not a great idea to try to kill it).

Thank you for reading my Cassiopeia guide, and I hope you've learned something about her. Please leave feedback and if you think there's something I should add, let me know and I'll try to do it. Oh, and warding is a good thing. I may add a section on good places to ward later.