I know people don't like Teemo very much but
TL;DR at the bottom for those of who with the attention span of the rodents that likely feed off the leftover meal in the fridge because you don't want to bother cooking something. Smh. Totally not me.
After getting rid of a lot of the "this champion isn't trash" syndrome as a person who mains Teemo commonly will believe, I'm pretty sure it's time to admit Teemo is a flawed champion design.
A lot of people don't really understand the "why" however. I am extremely confident Teemo does not actually need a full scale rework even if he does need a VU.
I can smash my lane and also get decent "champion rank" scores at the end of the game even on trash games as long as I'm feeling up to the challenge and know what I'm building. Teemo is still viable in some cases. But I can't definitively make my opponent lose on my own even when SUPER ahead. This is something you'll see for many Teemo's, and I'm here to explain that "why." Summary at the end.
Teemo's kit Some things people need to realize for Teemo is that early game, he is not really to be messed with when he has the safety of his minions. Your champion has to be blatantly capable of ignoring the wave or brute forcing Teemo in order to properly punish Teemo, and since he is in top lane, this potentially includes champions like Darius, Tryndamere, etc. who Teemo is seen as a counter to. This will come off as ironic to most people but expected for Teemo players with experience, simply because lane bullies do not have as much power as they used to.
Meaning, Teemo's kit is not actually bad for lane phase. At least, not initially.
Toxic Shot is Teemo's bread and butter and enables his entire lane phase. It is auto-reliant. Keep this in mind. If he can't walk up to make an extended trade, then he will likely lose the upcoming trade if anyone is capable of returning fire. And since Teemo has no sustain built into his kit, it severely punishes him. So despite the Blind for peel against fighters, he doesn't really have the tools to handle problems in the lane, if any were to happen. The strategy to beat Teemo commonly is to just camp his lane, since he not only loses power but can do nothing about it, lest he wants to die for it.
Move Quick does nothing but give movement speed, but carries an outrageous cooldown, lessening Teemo's pressure despite it not giving any other bonuses or slow cleanses. It is most definitely the weakest part of his kit, and shrooms end up being the strongest part with huge flaws in activation speed and general range of effect (try detonating one on someone who is already within your range, I promise you competent enemies will not make it easy for you).
Teemo's builds
For a champion that lacks sustain, Teemo builds often go all-or-nothing for damage. "Kill before you are killed." This sets Teemo up for aggressive plays and sometimes successful snowballing, especially when the enemy seems to lack any kind of awareness of what Teemo wants to do versus what he actually can do. However, typically if the Teemo is ever behind, he is useless and dies quickly using this build. Even when ahead, it is hard for him to kill targets with only one Q and one auto, and I would like to believe so because that'd be broken otherwise. Naturally however, that's all Teemo really has other than shrooms.
A popular build for high elo Teemos, one that I'm using myself, is to use Hextech Gunblade to force sustain into Teemo's kit. This is extremely potent because Teemo's Toxic Shot is considered single target, and shrooms create great sustain opportunities. Bilgewater Cutlass gives you lane sustain and all-in potential Teemo normally lacks, and then finishes into a wonderfully amazing sustain item that early game is comparable to a Warmog's when you have targets to heal off of.
This is not always the best choice for snowballing, but it has INSANELY reduced risks for the Teemo player in almost every circumstance compared to anything else he could possibly build. Yet, it is not a popularly bought item because it does not show up in Recommended Items.
Here's the fun part however for Teemo after the Gunblade. What is actually "good" for Teemo afterward? If you took Liandry's, it'd be garbage at that point for the simple reason that Teemo does not have cooldown reduction by the end of his second item. For those of you who do not know, this means Teemo has no CDR for skirmishes and objectives. Not always bad, but for Liandry's specifically which relies on ABILITY CASTS to be useful as a purchase, it is extremely inefficient.
Alright, next. An attack speed item then? If Teemo goes an attack speed crit item, his DPS goes up, yes. But poison cannot crit. This means he is weaker than crit champions by this point if he decides to itemize that. However, if Teemo is attacking faster, it looks to be superior at surface value.
As for attack speed/AP, aka Nashor's Tooth. The components are slow for that point in the game, and Gunblade is not a cheap purchase. You'll be sitting on weak component items until it is done. That is why I believe AD-heavier purchases reflect better on Teemo. Let's compare purchases:
= 6100g, and all of Teemo's spells deal significant damage. No sustain.
= 6400g, but Teemo's spells have mostly fallen off due to lacking %HP damage. Nashor's Tooth is also not healing Teemo for much at this point to pair with the build when it's finished. But, his autos still do damage.
= 6000g. This not only finishes earlier than the other builds, including the one using Gunblade itself, but also makes Teemo tankier as stated. The most important thing is the unit collision, giving Teemo absurd power if he won lane, because it is hard to contest him in a side lane. As Teemo would rather fight 1v1s, better splitting tends to be the better option.
items = variable but more expensive than others listed here typically unless taking GA. Since Gunblade heals for ANY damage dealt, and Teemo is damaging via auto-attacks, BF sword items tend to be the best items to go into after Gunblade despite Teemo being an AP champion. (Note below)
= 6100g. Takes the strengths of Gunblade and immediately dives into burst while ignoring MR a bit. Same effectiveness as path above for average damage dealt in a fight but since it does not have attack speed and does not have mana, it is generally worse when behind and is weaker when taking dragon, baron, and jungle camps. Stronger against towers. Unlike Nashor's Tooth, you will sit on components that deal damage.
//For those questioning "how is that possible": Teemo's Toxic Shot is his bread and butter. However, as League has evolved, damage has MASSIVELY inflated in the game. Meaning, the secondary damage from your E typically leaves you with a Toxic Shot that rarely goes above 120% AP ratio in a given fight on its continuous hits (meaning fights do not typically last above 12 seconds against one champion). Therefore, Liandry's/Nashor's Teemo is not getting the full value of Teemo's AP purchases unless he lands a shroom in a fight, activating all of Teemo's synergies. But more importantly, Teemo would be lucky if the target survived even past 6 seconds without escapes, deaths, etc. already having happened.*
On-hit Teemo relies mostly on Toxic Shot's base values because it does not buy Nashor's Tooth. Teemo therefore is not getting superior purchases to AD items because on-hit is only making him attack faster until they are completed. This is only made worse with Guinsoo requiring a ramp-up and the recent nerf hitting Teemo's power with the item.
The conclusion I've drawn from all this collected information (along with my in-game experiences) is that Teemo is a one item powerspike champion, and falls off slowly as the game continues. If Teemo's team stalls long enough, then his builds come back online at 3+ items, but the journey to those 3 items is extremely rough after the first item has been obtained. Gunblade + raw stat prevents Teemo from falling off. He is not very good vs. tanks, but that is where attacking more often (on-hit) is better.
What does this means for Teemo then?
Well, unfortunately, this means Teemo is a bad champion. As I declared.
There is no efficient route for Teemo to build Gunblade into raw stat and keep enough attack speed to be properly ramping up. Nashor's Tooth's components are absolutely garbage because they do not add on-hit damage early on, forcing it oftentimes to be a second item but with a terrible farming requirement. Meaning, even though it SHOULD be Teemo's next item, its components are not good enough. Yet, Nashor's Tooth remains a core item in many Teemo builds. Gunblade does not. It damages the champion severely for less experienced players, and Teemo does not really have a true solution to his problem even while supposedly "solving" the problem.
And of course, Toxic Shot is too slow for the game now. Blinding Dart could go on very well unchanged, but both Move Quick and Toxic Shot are what make Teemo weak unless his numbers are overtuned. My suggestion is to do something to make Toxic Shot's ambient damage turn into active damage like Udyr or just empower it situationally when fighting champions and attacking them fast enough.
Someone suggested cleansing slows when activating Move Quick. I agree with that suggestion.
I also do suggest moving Blinding Dart to Toxic Shot as an active which scales on Teemo's base AD and making Q the new stealth, but allowing his passive to remain as attack speed with the bonus halved unless exiting stealth. Max duration of stealth moved to 30 seconds to prevent trolling. It's a thing of beauty to see trolling permastealth Teemo's. Too beautiful for us feeble-minded players.
Lastly, something added to make Teemo's shrooms explode when an enemy is within ~300 units of him for tight situations that do not normally allow him to have a 4 ability kit, along with possible auto-attack synergy would be GREATLY appreciated to have less people in Teemo's ass. It's like Teemo came straight out of prison, cut the guy a break.
Alright. Now the time we have ALL been waiting for.
TL;DR Teemo is the best champion in the game of all time, all hail Teemo.
The end. Teemo's itemization routes are inefficient after first item, and Gunblade is arguably his best first item but isn't in his recommended builds. Toxic Shot, Teemo's core ability to level, is outdated because it is too slow in today's league, and likely should get an update similar to Udyr's Tiger Stance. Move Quick should cleanse slows off Teemo to prevent an already linear kit from being useless if it interacts with soft CC. Shrooms need auto-explosion potential when someone's face is up your ass already, and possibly better auto-attack interactions. That's all, thanks for reading.