Hi my Summoner name is Tsasuki and I'm a lvl 30 with somewhere around a year of experience in LoL, also playing HoN.
While fooling around a bit with some friends, one of them suggested I'd play Cassiopeia as an AD Character, rushing triforce and getting some nice AD. Me, being bored of all my current standard building of every champ, decided to give it a go, since she deffinitly had all the pro's a great AD carry should have, and have been winning and doing lots'o killing with AD Cassiopeia since.
If this guide get's some positive feedback, I'll go some more in-depth.

Pros;
- She has everything a good AD needs, and more:
- A good slow with a Dot to spice it up a bit
- A good skillshot Dot with great chasing capability because of speed bonus on hit
- Spammable skills for triforce procs
- Very good farming capability
- AOE stun/slow
- Great attack animation
- Dot's remain a great source of damage due to spammability, while devastating the enemy with your auto-attacks.
- Everyone will laugh at you when you say you will go AD, which turns into admiration pretty quickly


Cons;
- a bit squishy
- you tell me?

: Your passive, makes getting mana items other than your sheen/triforce unnecessary. Great passive.

: Hitting this on an enemy champion will give you a speed boost, as well as doing some nice DoT. This is great for chasing/getting away or increasing your overall dps.

: This, along with your Noxious Blast is what makes you such a great farmer. It also has good utility like you Q, slowing your enemy and dealing some DoT.

: Not so great damage on this built, but will allow you to proc that trinity force every single time it is up.

: Your ultimate. It is awesome both offensive as well as defensive. Hit the enemy team while they charge yours to instantly turn the fight around.

When playing Cassiopeia I highly recommend you learn how to Smart-cast your spells. It is done by holding shift while you press the button (IE: Shift+E). This will cut out the targetting phase of your spell, allowing you to spam more efficiently.

As AD Cass, it doesnt matter what lane you take, your farming capability is great, and you will outfarm anyone regardless of your lane as long as you play with some common sense.
When laning, it is best to go with a supporting character, allowing you to get (nearly) all last hits, farming up your triforce ASAP. I will mostly have triforce completed at around lvl 10 along with zerker greaves.

Never underestimate your Miasma (W). It's dps might seem low, but it slows the target pretty nice, allowing you to easily hit your Q and/or land 1/2 auto-attacks giving you a great harrassing early. Dropping this on your own minions will effectively mess up any melee champion's farm. Again, the key to Cassiopeia earlygame is farming up that trinity force ASAP.

When you get the trinity force and your zerker greaves, the real fun starts. You will be devastating minion waves and together with your Q skill (just shoot it at air/minions) and the triforce procs towers will be no match for you either.

Gank some, push some, and farm up that infinity edge. When the teamfights come, spam your abilities for decent AOE damage/slowing while you auto-attack anyone who foolishly gets too close to your team down in a matter of seconds.

If you see the enemy team charging yours, dont be scared, turn around and blast you ult in their faces, dealing good AOE damage and stunning/slowing them, allowing you and your team to litterally shred their carries apart.

I use Ghost/exhaust combo, for obvious reasons.
I can also see Flash and Teleport as viable choices

I get my items in this order:

Start:
Doran's Ring/Blade : Choose whichever you like, i prefer the blade for the extra ad, doran's ring is good too to give you some bonus mana-regen and a bit more AP to spice up your skills a bit.

Depending on how your doing, at your first back you should be buying:
boots of speed: for obvious reasons

Zeal/Sheen: Whichever one you prefer, most of the time I'll be able to afford both at my first back.

Berserker boots

Trinity force: Your spammable skills will proc this a lot, and stat-wise it gives you a very nice base to build off.

Infinity edge: More damage, more crit, more kills. 'Nuff said.

Guinsoo's Rageblade: This will get you some nice attack speed, along with some bonus AP for your skills.

Most of the time the game will be over by now, but if your still going, you can consider these:

Hextech Gunblade: AD dmg, AP dmg, lifesteal and spellvamp. Allways a good item for hybrid-like characters

The Black Cleaver: Attack speed along with damage and an armor reducing debuff will make even tanks perish before this Medusa.

With this build i have been able to 1v1 and even 1v2 anyone whose name isn't spelled like M O R D E K A I S E R. Or any other fed tank.
In teamfights you are a beast, stunning the entire team for 2 seconds, slowing, dotting (runners will often die because of this) and auto-ing down everyone.

Feedback (both positive/negative) is appreciated, this is the first time I write a guide. I wrote it because I felt the way I play Cassiopeia is kinda unique.
Try the build before you QQ about it, chances are likely you'll like it.
Comment/Rate please! :)