Hello LoL Community!
I am Fuzy Wuzzy, and this is my very first guide! So i can asure you, there will be mistakes, but i'd like constructive criticsm.
I've never played Teemo alot, untill i heard the story about Hunter, if you haven't heard it, i'd suggest visitting this link: http://eune.leagueoflegends.com/board/showthread.php?t=511414
I shed a man tear that day..... He will scout ahead....
I played Teemo constantly after that, and he quickly became a really nice little fella, though i mostly play Dominion, as i cba to play 45 minutes for 1 game :P - Anyways, i hope i clarify myself in this guide, English is not my mother-tongue language.

Pros
- Great mobility
- Decent at shutting down AD's
- OP Passive
- Insane DoT
- Small "wards"
- Alot of viable items

Cons

- Easily nuked by AP's
- Is a wandering global taunt
- Not the greatest range
- Magic Resist is a complete shutdown (If AP)
- Might recieve hateful comments from teammates.

Flash: Is in my opinion one of the (if not the) best summoner spell, even after the nerf, i still find it really usefull on Teemo in Dominion

Ignite: Adds alot more DOT in combination with Shoorms and Dart. Also i feel it's a must in Dominion!

Ghost: Also, one of the best summoner spells in Dominion, if you dont like Flash go ahead and take this instead.

Teemo can be played as AP, AD or Hybrid, which opens ALOT of different playstyles for this little fella, but this is the items i have had the most succes with in Dominion.

Starting Items:
Pretty standard in my opinion, Kage's Lucky Pick instead of Prospector's Ring gives you an advantage imo. You can get your other items faster, though, you're a bit more squishy through rest of the game. Bear in mind, you can take Mana pots too, though i usually back, when we or the enemies have captured top.

Core Items:
Wheter you get ' Stinger' or ' Fiendish Codex' first, is all situational. I believe Blackfire Torch is a part of his core, because it gives you all the damage you need to be a really effective Teemo, though you can take Wooglet's Witchcap instead, giving you the active, but less damage. - After these items, your game might be over, but here are some of the situational items.

Situational Items:
I rarely get to finish these items in Dominion, but sometimes, it does happen.

Deathfire Grasp: Adds a nice burst, and a nice bunch of AP

Frozen Mallet: Adds alot to your survivability, though it's not that effective.

Hextech Gunblade: Also adds nice burst, AP & AD mixed with Lifesteal and Spell vamp is really nice!

Kitae's Bloodrazor: Adds damage to your already really high AS.

Rylai's Crystal Scepter: Adds surviability and an extra slow, decent AP gain too.

Wit's End: Adds nice AS and some survivability.

Wooglet's Witchcap: Might give you just enough time, for someone to die from your Ignite-Dart-Shroom combo.

Void Staff: Pretty self-explanatory, easy to build after core items, nice AP Pen.

Abyssal Mask: You often stand still between 2 capture points with your shrooms covering the area, shreds some of their magic resist and gives you a bit more tankability against other AP Chaps.

Morellonomicon: Gives you 20% more CD Reduction, really great item on shroom-camper teemo.

Toxic Shot is your main ability untill you hit level 6. Though i really like maxing Blinding Dart right after, a skill in Move Quick can make a big difference.
R > E > Q > W

I get that one point in Spellsword Just because we will end with a good amount of AP. I get Durability and Hardiness going 21/7/2 since AD-Bruisers and Assasins tends to be better in Dominion ( Pantheon, Talon, Olaf) - Also 2 points in Wanderer for faster roaming with shrooms!
I don't get Summoner's Wrath , cause i dont see the big difference with the 5 xtra AP when Ignite is on CD, though, if you take Ghost over Flash, i would take this.

How do you work with your team as Teemo?
If you can't co-operate properly with your team, you will have a rough time!

I usually try to use Blinding Dart and auto-attacks whenever they try to capture it. As long as you stay with your team, and only moves forward to poke, you will do fine.
Though if you get caught, use Flash and Blinding Dart that will mostly do the job, and your teammates can easily catch your enemy(ies)

Just remember: When you play top in Dominion, it's about POKING your enemies, as long as they dont cap, you are slowly winning top.

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After level 6

You really want to be a pain in the butt!
Bear in mind, you should only place Mushrooms here, when you have top! Prioritize that!
It's also here you want to use your passive, to wait for your enemies, when they pop 1 of your traps!
Below is a picture of places you want to fill with shrooms:
Red dot: Spawn / Base
Green dots: Mushrooms

I think that was all, i tried to make it quick but still informative guide. Constructive Critiscm appreciated! Teemo is super funny when you get good with him, i had so many laughs with my friends, i still play him once in a while, and i rarely do bad with him, and here you have the proof!

Good luck outthere summoners!

PEACE!