Hello everyone who reads this guide. This is my first guide and would like to make this a great guide by getting some feed back from anyone who tries this build out. As many other people I first played Teemo when I started playing League and loved his kit. I also loved the way he can massively place mushrooms and annoy people. I think that this type of Teemo can really be much of an annoyance. This build is made to basically deal true magic damage early on to gain a good advantage. This build is a really big threat to those who don't like to buy magic resist items just because they don't think it is necessary. The win rate for this build for me so far in normal queue is about 70% with in 30 games. I can't guaranty the win rate because some times fat is just against you. However don't think every game will go as you hope but hey that's life, always full of wonders about the future.

Pros:

-Tanky
-Deals lost of damage
-Nice penetration if you know what I mean
-Lots of poison damage
-Mushrooms hurt alot
-Easily carry when fed

Cons:

-Can still have bad games
-Hard to come back after a weak start

Taking all Quints and Marks for m. penetration will be key to how this build will work.
If you find it necessary you can also take some armor seals if you feel you need to.
Hybrid penetration runes are also viable if you want to deal more damage with your auto attacks to help you cs with more ease.

I take the standard AP tree with Both armor and magic pen because he wouldn't be a real penetrator with out penetration. For the defensive tree i take the standard 9 that people usually take to help improve your sustain.

Why go for this type of build? Well with this type of build it utilizes the properties of each item. The passive from Liandry's Torment really helps you hurt enemies as well as gives you penetration. The boots well they are generally for penetration obviously. The Abyssal Scepter is main;y used just for it's aura. It can also really help out if you are laning against an AP top.
Next I like to get a Nashor's Tooth or Wit's End to improve your attacking speed as well as provide the nice passive they give. For the 5th item it can be either a Rylai's Crystal Scepter for the nice slow effect and hp or a Warmog's Armor to just improve your sustain. If you feel like you need more armor you can also try to take a Randuin's Omen instead of a Warmog's.

With the high penetration and ability power runes you are almost certain to start off strong if not stronger than your opponent. For the most part just try to cs wile at the same time try to poke them out of lane with a blinding dart. Since most top champions usually go AD the blinding dart usually helps enemies stay away or just down right become afraid of trying to trade with you.

For the most part i try not to overextend my lane unless i know that the enemy jungler is not near or no were to be seen. Due to Teemo's global taunt I like to play it safe as possible.
Once I reach level 6 to get his most annoying weapon I place them all around the areas where a typical jungler would try to gank from. Wards are still essential to have even with your mushrooms, it can some times not be enough to see an incoming ganks that can possibly be from more than one person at a time. Better safe than sorry imo. Flash as usually can help avoid getting ganked as well.

By now the game should have progressed enough for you to be a major threat if you can stay behind your team in team fights. If your laning faze went well you should be able to carry the game with out much of a problem you should have your core finished or almost finished. Try to kite people from behind your team to ensure your survival before you tank up. As usual always try to save some mushrooms to put in obviously highly used paths to anger your enemies. Mushrooms can also help save you from people who try to chase you down by being placed in an appropriate area.

As stated in the chapter above try to kite enemies from afar due to Teemo's low heath at first. By staying near the back of the fight your chances of winning the team fight increase greatly as you punish people with your poisonous darts and mushrooms. Once you start getting more tanky don't be afraid of staying a bit closer to the fight due to you have such a greater amount heath
compared to your early game.

Like any other champion if fed enough you will be able to carry the game and win it. With your massive amount of heath increase to survive will help more instead of just buying more AP to improve your damage and dying off way too fast in team fights before you can really do much at all.

I have yet to try this out in a ranked game but will try it out soon. More updates to come.