Before we begin the amazingness that will be Teemo, let me say a few things. First of all, this will not work for everyone, so do not be surprised if this takes you on a new route with Teemo. Secondly, this is mainly used for mid, though I will detail how exactly to perform on top or bot. And lastly, third, this guide will, if you follow the battle, will get you to at least a 15-0-? stat, at least. This took me some time to amass together, combined with practice and lots of trial and error. It's simple and not visually appealing, I know. But it's supposed to be that way for its a straight forward build. Adapt to the battle with the above masteries and items and you should be fine. I sincenerely hope you enjoy this build. Please leave comments as to how it can improve and what not ^^

What you see above are the MAJOR runes you should have. This guide provides a bit of leeway seeing as how Teemo is very flexable in game. Teemo is at his best if you up his Att. Speed to at least 2.5. That's two and half hits every second, and believe me, with Toxic Shot in play, the enemy will crumple. Even if Toxic Shot is the one you worry least about, the amount of uped damage from the runes will also serve to help you well. I recommend a few mana ruins as well, if nothing else but for your Mushroom Laying Self, or MLY :D.

What you see above, in the masteries, is almost a completely aggressive build. Reason being is that Teemo can do high amounts Burst DPS then retreat before the enemy even knew what hit him. Due to this, the mana ruins in above chapter are acceptable to have, and justified at that. With the item set as well, the mastery for more damage against minions will have you raking in gold by the time you hit 10. Defense is light due to the fact that you should try not to get hit too often, using your mushrooms by 6 to cover your escape and leave your enemy ripe for the picking.
Now onto the spells. One can see that the aggressiveness goes to the spells as well. Early game, Ignite is your best friend when you want to score that 300 gold per kill as well as send your enemy into a retreat to regain health. Flash, of course, is what you always would need in your arsenal. Both a great attack spell and retreat spell, it's nigh holy. Stretching the limitations would be using Exhaust instead of Ignite. If done right, your att speed will hammer the enemy down to 0 within a few seconds. It can also stack with the side effect of your shrooms.

Simply put, it's sorta obvious. This can help you farm your way to power, which is why Ionic Spark is here. With it, you zap three targets with magical damage every three hits. It's awesome at high levels, when a running enemy is zaped then poisoned, usually leading to a kill. It also helps reinforce Teemo's att. speed, the vital part of Teemo in this guide.
The bad part of this all is that by the end, you only have 2k of health. This means you must run when confronted with a whole list of baddies unless your mushrooms injure them severely and you can take pot shots. But, that is also why I list pots at the begining. If you take mid, these will help you maintain dominance over the lane and provide a tough time unless they gank. And that is a flaw. When ganked, Teemo is done, so place your shrooms everywhere so you can spy an ambush before it happens.

As you can see, you rest on the laurels of your poison. This can grant you kills and be devestating at mid and late game, providing you actually rank it up. You want to use Move Quick in case an AOE is active and your flash is done. Move Quick should get you out of harms way unless you're knee deep in cow cud. Blinding Dart is more effective mid game, where by now your item build should be beyond thinking. But use your basic with poison to cripple your enemy and provide assists where needed. Your shrooms are holy, and by every rate deserve to be. As in the words of a great player (Who's name now escapes me), if you have three shrooms in reserve, you aren't playing Teemo right. Not only can these drug-inducing shrooms be teleported on, they provide line of sight and can help you escape from a chase. Lay these things down like your sanity was on the line (For those who's sanity is lost, think about getting it back).