Greetings summoners!
The world of Runeterra is a brutal, unforgiving one. It is full of evil monsters that would end all life. But which faction is the most dangerous? Is it the all consuming void? The never ending death of the shadow isles? TEEMO?!? Vote in the poll below!
GreenLore3 votesOverall I'd say the 3 biggest threats are the void,the shadow isles and the watchers
All 3 of them look like they could be extremely powerful
The void doesn't seem that organized,but if malzahars visions are true,then they will come and consume everything.Not to mention that the atmosphere of the void seems to be extremely dangerous itself,what would happen if the voids atmosphere actually leaked into the world of runeterra?that would seriously mess things up
The shadow isles are also quite impressive,I mean bilgewater looks rather helpless against them.The harrowing allows them everytime to raid large parts of the sea and they can't do anything about it. And the more enemies they kill,the stronger they get,the next harrowing will be probably even worse than the previous one. However I'd say the shadow isles are at the moment still not that much of a threat,their growth in strenght is the problem,so they could become extremely dangerous if nothing is done against them.
Lastly the frostguard might be a tiking time bomb. The frostguard themselves might be strong,but I wouldn't consider them much of a threat.Their strenght is probably roughly on the same level as the winters claw or the avarosan(maybe a bit stronger,but not by that much),thats why lissandra doesn't take action. The dangerous thing though would be the watchers.If the frostguard managed to awaken enough of them,then that could cause serious troubles. I mean judging from greyors quotes,they were once able to conquer basically all of valoran with the help of the watchers.
Bonus points go to 
who could be more dangerous than all of the above together if freed from the sarcophagus that is limiting his powers,but his motives were always kinda vague,even before the retcon,so he might not be an actual threat
Laughing Fish1 votesVery valid points. And I forgot about . He is certainly a threat indeed.
BLU Medic2 votesI'd say it's a tie between the Void and the Shadow Isles. Both are slowly slithering their way in and corrupting the lands, and without the League, little is being done to stop them.
Laughing Fish1 votesVery true. The level of concern about the void is dangerously low. The Shadow isles is hard to fight, as every solider you "kill" simply comes back. They need to purge the entire island.
BLU Medic2 votesAnd don't forget, every soldier you lose is a soldier the Shadow Isles gains...
Laughing Fish1 votesExactly, which is why I voted for Shadow Isles as the greatest threat. I think the Void could kill millions, but they are so chaotic and uncoordinated that they would lose in the end. The Shadow Isles could end all life.
Sneak Dog2 votesVeigar. He is willing to crush all for his ideology. Teemo doesn't have enough ambition to do what Veigar does.
Laughing Fish2 votes
will attempt to swallow 
's soul, only to find out that Teemo has no soul. Instead of a soul, Teemo's heart is a never satisfied vacuum that will suck whatever is left of Veigers mind into the endless abyss of eternity.
Sneak Dog2 votesAh, foolish man. Veigar and Teemo are the same, but Teemo is content with merely Bandle City. Now, having achieved his goal, he hides his blackened soul behind a smiling mask and an indoctrinated phrase. Teemo and Veigar aren't above cooperating when their goals align.
Laughing Fish2 votesVeiger is powerful, but even he recognizes what he does is wrong. Teemo just keeps on smiling as children scream and cities burn around him. As the last sparks of life fade away, we will hear the same phrase being repeated for eternity in the darkness: "Never underestimate the power of the scouts code."
The IVth Legion2 votesTeemo is the worst enemy there is
Laughing Fish1 votes: "Size isn't everything."
Togekiss241 votesI' m surprised you left out 
Brand. Have you read his lore? He is literally the vessel of a fire demon who's set out to start a burning apocalypse on the world. The League is the only thing containing him (he's not really a faction but he's still pretty dangerous).
Laughing Fish2 votesThere are just so many threats lol. I just don't see Brand actually bringing down any of the other major factions though.
Togekiss241 votesHe can already 5v1 an entire team in-game (if fed), so I can see him bringing down entire cities. :P
But eh. I guess he does have a susceptibility to powerful magic provided he ever tries to go on a rampage.
Laughing Fish1 votesBrand could kill thousands, but he would still lose to an Army. Demacia defeated him fairly quickly, and only let him live if they fought for him in the league.
lightdragoon881 votesWhile the The Shadow Isles are creepy, they don't seem...evil. They just follow a difference lifestyle which is the afterlife. They aren't so much killing as changing how they live.
They even gave us the Pentakill band so they are not all bad.
So I would have to go with the Void since they just want to kill. Not change the world or change how one lives, but just to eat/destroy it and move on to the next world.
Laughing Fish1 votesThe Shadow Isles goal is the extinction of every living thing... That doesn't sound evil to you?
lightdragoon881 votesNot really cause they always say that the afterlife is a wonderful place.
It almost like they are a religion and are convert people to it. Actually it is with Karthus:
http://images.wikia.com/leagueoflegends/images/5/5e/Karthus.start03.ogg http://images.wikia.com/leagueoflegends/images/d/d0/Karthus.start02.ogg http://images.wikia.com/leagueoflegends/images/2/26/Karthus.attack05.ogg http://images.wikia.com/leagueoflegends/images/a/af/Karthus.attack15.ogg http://images.wikia.com/leagueoflegends/images/0/07/Karthus.move04.ogg http://images.wikia.com/leagueoflegends/images/2/20/Karthus.move17.ogg http://images.wikia.com/leagueoflegends/images/a/a3/Karthus.tauntLucian03.ogg http://images.wikia.com/leagueoflegends/images/0/03/Karthus.tauntMordekaiser01.ogg http://images.wikia.com/leagueoflegends/images/f/f8/Karthus.tauntThresh02.ogg
Laughing Fish1 votesKarthus is a lich. He is a being of pure evil that attempts to use his words to convince the weak minded that he is telling the truth. The extinction of all life in the world is not converting people to a religion. Being good with words doesn't make you a decent person. The Nazi's were masters of using their words to convince others they were telling the truth, but that doesn't make Hitler is a good man.
lightdragoon881 votesCan't argue with that...but I still find the Void a bigger threat.
Laughing Fish1 votesWell the void is certainly worse. The void is obliterating everything. They are not just ending all current life, they are ending the possibility that any life will ever return to that entire dimension.
Sneak Dog2 votesKarthus supposedly ate a poro on stage, live! A live poro! shudder Some even say that the poro wanted to attend every pentakill concert and Karthus simply gave him his wish.
Der Lindwurm1 votes
"Muahahahaha... all is proceeding exactly as planned..."
Laughing Fish1 votesThe Black rose is certainly deadly, but they are not planning to destroy the world. They dream of a world where the strong are not bound by the weak. They wish to rule the world, not kill it.
Der Lindwurm1 votes[{quoted}](name=Laughing Fish,realm=NA,application-id=6kFXY1kR,discussion-id=7yaiXOm9,comment-id=00060000,timestamp=2015-01-21T17:33:37.028+0000)
The Black rose is certainly deadly, but they are not planning to destroy the world. They dream of a world where the strong are not bound by the weak. They wish to rule the world, not kill it.
But that's all part of the plan! Get everyone worried about other more obvious threats. Let them believe the reign of the Black Rose "wouldn't be that bad" in comparison.
Laughing Fish1 votesOh they are certainly bad people. But The Black Rose winning, while certainly not a good thing, would not end the world. It should still be fought, as they are still evil, but their victory would simply mean that the earth was living under a brutal regime. Life would still survive, but it would be less rich and meaningful.
The Soulforged1 votesKarthus decides to sing requiem... gg every living thing
Laughing Fish2 votesExcept is not alive. Nor is Teemo dead. Teemo is the incarnation of pure, unrepentant sadism.
The Soulforged1 votesYes. Teemo is undead, but teemo is hardly part of this world. He is exactly the opposite. He is the opposite of what this world is about, and such he must be purged.
Laughing Fish1 votesTo say Teemo is undead implies that he was ever alive.
The Soulforged1 votesWell, I don't know how to define him really. He's just kinda... Satan.
Ebonmaw Dragon1 votesThe most Dangerous?
Technically... 
... if he decides to take a vacation for a second they all will be DOOMED.
is also Dangerous... i mean, he is stupid, insane, evil, and has tons of magical power... im sure that he could destroy a whole city if he wanted to. Also, is capable of corrupting Bard in theory.
Ironclad Dragon1 votesThe Frostguard themselves aren't as much a threat as the Watchers. It'd be the Others/White Walkers all over again. Thing is with the Shadow Isles, undeath is another state of existence. A ghastly state, but an existence. The Void wants to wipe you from existence.
lucklylee1 voteswhere dafuq is shurima? azir is an ancient king with the power to control sand goddamnit. sand is in the soil too. so he could basically use it anywhere
also +
Laughing Fish1 votesThere was no Azir when this post was made.
Matezoide1 votesThe Shadow Isles mostly mind their own business until the Harrowing. The Void seems to be far more active at actually destroying the world, so they get my vote.