Hello, and welcome to my first guide here. I want to share an unusual, but what seems an effective way of building Teemo as a hybrid/more tanky build. Teemo is often focused in teamfights, and if built pure dps is very squishy - this guide will eliminate that problem, and give you some nice dps on top of that.

(Require comment to vote is turned on, in case anyone tries to vote and finds they cannot. Criticism and feedback is very useful to me and as such I have turned this on.)

Runes:
9x Greater Mark of Magic Penetration - improves your Q, E and R, very useful for increasing dmg
9x Greater Mark of Scaling Cooldown Reduction - more cooldown = more mushrooms = wrecking the map.
9x Greater Mark of Scaling Magic Resist - you're going to (hopefully) be more at range than in melee, so its more magic spells that are going to hurt you - this will help vs that.
3x Greater Quintessence of Health - Helps a lot early game.

Standard 9/0/21 build - you can switch out improved exhaust for 1/3 deadliness if you want a different summoner spell, same for Blink of an Eye if you want, for example, ghost, you can s*** it for Haste .

I believe this benefits this build the most as the majority of your damage comes from the magic side of things, so the 15% magic pen really helps with that. Coupled with the improved flash, the magic regen (which Teemo really needs) and CDR (which this build lacks a little of) it really rounds off this build.

Blinding Dart - your main skill you want to level first - puts an enemy ad champ out of the action for 2.5s at max level, which will mitigate a lot of damage. Also a nice poke spell.

Toxic Shot - a very powerful poison - I've got a lot of kills with this when the enemy champ is running away on very low hp and I manage to get a hit off on them. For the best creep wave clearance, use on every minion once and watch the poison kill them all off.

Move Fast - this is what enables Teemo to plant mushrooms everywhere without losing out on a lot of xp/gold and be able to gank people, and escape ganks (if you see them coming - it's cancelled if an enemy champion attacks you). Much needed on Teemo, as his base move is kinda slow.

Noxious Trap - this is why you play Teemo, right? This is why you rage and froth when you're against Teemo. Cover the map with these little things and reap the benefits later. Many a time have I laughed when a trap I placed 10 minutes ago explodes on a champion who's just got out of range so I or my team can catch them, or I'm about to be caught and the enemy champion who's running after me runs over it, enabling me or another teammate to get away. Guaranteed to make the enemy team rage if you place them correctly. Common /all's:

"omg mushrooms ffs"
"noob mushrooms lucker" - after I got away with low hp with 4 or 5 enemy champs following me through a trap.

...you get the picture. Map included, taken from Clairabelle's Teemo guide (thanks!).

Flash - cannot say how many times this has saved my life in LoL, not just on Teemo, but any champion. Extremely useful spell, especially with the mastery Blink of an Eye .

Exhaust - Teemo does not have any inherent slow, and doesn't like enemy AD champs, so this will definitely help you to gank and help you stop being ganked. Great with the mastery to improve it.

Other options instead of exhaust:

Teleport - if you take this, take the teleport mastery on the top tier instead of 1/3 of Perseverence . Can be very useful if you're solo/mid laning and want to get back fast - you can also teleport to your mushrooms, which can lead to some nice ganks and could potentially save a team mate who's being chased.

Heal - could be useful for newer Teemo players - can help you to stay in lane much longer and could potentially turn a first blood or teamfight around.

Cleanse - potentially a very nice option - cleanse then W to run away means most champs won't be able to catch you unless they manage to pop another slow on you straight away, or you have MF/Yi on your tail.

Ignite - useful if you're vs Mundo/Swain/Warwick, otherwise I don't find this one all that useful, you have your W if you need to catch someone to finish them off.

Ghost - can see some use for this spell if you find yourself up against Yi/MF and wish to get away, Flash into the jungle, Ghost + W and run away as fast as your little legs will take you. Reasons why I wouldn't take this are the same as ignite - you have your W already, and I feel Ghost would be overkill.

Summoner spells not to get:

Clarity - This will really only help early game and will be fairly useless late game, especially with your Nashors.

Rally - no, you aren't an AD champ, you're hybrid.

Fortify - save it for tanks/support.

Clairvoyance - much better on supports.

Smite - wut? You aren't a jungler.

Revive - facepalm.

Ah yes, the interesting part.

I've had many people, when I start a game with this build, going "wtf, warmogs on teemo? lol". Ignore them. They'll quickly realise that you're actually a deadly force to be reckoned with, especially after you have your Atmas.

This build is designed to bring a lot more survivability to hybrid Teemo, whilst still keeping a lot of the dps intact. You can be at about 3k hp by mid game, which with Mercury's Treads means a lot of survivability. You usually end up with about 3.8k hp endgame, with the ability to absolutely decimate enemy squishies.

Start with a Regrowth Pendant and a Health Potion. This will enable you to stay in lane for a very long time, even when you get low on hp - just pop the potion and let it, and the pendant, do their work. When you have the gold, port back and grab a Giant's Belt and Boots. If you aren't doing so well, grab Boots and Ruby Crystal and maybe a ward. When you can, port back and grab a Warmog's Armor and Mercury's Treads.
Now you have some great survivability and will be quite hard to kill. After this, the game will soon evolve into the midgame, where there's a lot of ganking and roaming involved. Port back as and when you have the gold to buy some useful items. I put Cloak of Agility before Atma's Impaler because if you need to port back before you can afford the Impaler, you need the extra damage.

The rest of item sequence is fairly self-explanatory - I have not put a 6th item in. This is largely because although effective, this is a fairly expensive build, and you will not usually have the time to put together a 6th item. Nevertheless, I will put a few choices below which I think are good ending items for Teemo. Don't forget to buy all the potions once you have your 6th item and are still raking in the gold (if the game ever gets that far)!

Bloodthirster - if you're raking in the kills and managing to avoid getting killed late game, this is a very nice item which makes you nearly invincible with your huge health pool, as you'll be gaining a lot of life back with your attacks. Don't buy if you can't build it - you're wasting a lot of its potential

Banshee's Veil - a nice defensive item for blocking Karthus ulti, Amumu's Bandage Toss, an initiating slow on you, and a plethora of other skillshots and abilities that would otherwise mean you would die. Recommended if your team is getting beat on from a heavy dps enemy team.

Quicksilver Sash - very underestimated item; gives you a cleanse which even removes Malzahar's ulti, Ignite, Warwick's Infinite Duress and many more. Very useful if you find yourself getting CC'd a lot and the enemy team has a lot of magic damage.

Black Cleaver - very nice item if the enemy team is full of squishies - will reduce their armor a lot and gives you some nice AD on top of that. Doesn't synergize so well when you're creep farming with poison, but by this point in the game that shouldn't matter.

Trinity Force - I'm not so sure on this one, but it has a lot of nice stats on it which all benefit Teemo. The slow is also extremely useful, as Teemo doesn't have any inherent slow.

Guinsoo's Rageblade - gives everything a hybrid Teemo needs - AD, AS and AP! Although it does require some build-up to reach full potential, it can potentially be an extremely useful dps addition to your items.

Feel free to suggest additional items that you think would supplement this guide well, and I will consider adding them!

Thought I'd give y'all some proof that this build works, and produces some nice scores. :)

I hope you enjoy this guide, and get some nice games as hybrid/tank Teemo!

If anyone has any suggestions/feedback, please, write in the comments section below.

GL and HF!