PROS:
-Farming benefits AP, armor and gold.
-Amazing mid game, Unstoppable late.
-Can win any 1v1 encounter from mid game and later.
-Ulti extremely useful in teamfights.
-Hard to get ganked, nice escaping mechanisms.
-Ranged tank.
-Amazing gap closer and champion repositioning skills.


CONS:
-Weak early game.
-Can't take armor from levelling up.
-Farm reliant.
-Thornmail or blind may shut you down.
-Underestimated.
-Needs training and experience as Thresh.

Hello! I am a Silver 4 player of EU West with a lot of experience in top lane and jungling champions. At first i bought Thresh for a supportive role, since he is very strong in bot lane. But the more I was playing and learning him, the more i realised that Thresh's potential is far greater than a simple support's. Take your time and read this guide carefully, since I will explain many things about how you must play Thresh and dominate your enemies in top lane.

First of all, let's start with your passive, Damnation. For every soul that Thresh absorbs, he gains armor and ability power. At first, with every soul you gain 1 point and as you absorb more souls this percentage decreases. Eventually, around 70-80 souls you will take 1 point of armor and ability power for every 2 souls and this percentage will not decrease more. This means only one thing: farm like a maniac in early so you can be safe in late. Souls can be collected from minions and champions, but their appearance frequency is random. This passive also makes Thresh a natural hybrid champion.
Secondly, your first ability, Death Sentence is your main source of damage and Thresh's power. Passively, the longer he waits between attacks, the more magic damage he will apply with his next basic attack. This means that with his basic attacks Thresh deals both magic and physical damage, something really useful since most players buy armor in top lane. When activated, Thresh throws his chains, binding the first enemy or minion hit and pulling them towards him. If activated again, it will transport Thresh next to the enemy champion. This ability needs practice, like a Blitzcrank Rocket Grab so you can know how to use it effectively, because of its high mana cost and long cooldown. You must max it first.
Next, your second ability, Dark Passage is an amazing utility. When activated, Thresh throws his lantern in a range around him granting a shield that absorbs damage to any ally that approaches it. To start with, the lantern can absorb fallen souls from a distance so that you don't have to risk exposing yourself to an enemy gank or poke. Plus, the lantern reveals a small are around it, something useful for checking bushes. Not only that, you can use it to save an ally from danger, shield yourself in 1v1 encounters or bring your jungler next to you for more effective ganks. The only problem is its somewhat high mana cost and long cooldown, so it needs practice to learn ow to use it properly.
Your third ability, Flay is an amazing skill for repositioning enemy champions. When cast in the direction Thresh faces, he will deal magic damage in the area of cast and throw enemies away from him. When cast in the opposite direction, Thresh will pull the enemy towards him. Use it as a combination with Death Sentence for a nice amount of cc and magic damage. Also, try using it to throw enemies on the walls of your ulti.
Last ability is The Box. Thresh creates a box around him and when an enemies touches one of the walls, the wall breaks dealing magic damage and slowing the enemy by a high amount. Use it as a combo with Death Sentence and Flay.

The way i play Thresh, he is a ranged DPS tank with high armor. When starting the game, remember that Thresh is relatively squishy in early game and he isn't doing so much damage. Your main strategy in the first minutes is to farm with last hits and take as many souls as possible. Use the passive of your Q to effectively poke the enemy champion. After you buy Blade of the Ruined King, feel free to begin your attempts to get your first kill. In mid game your strategy should be something like this:
-Poke the enemy until his HP drops at 4/5 of his basic Health (losing some of your HP won't do harm, use it as bait since you got lifesteal)
-Execute a combo with Q, R, E to root the enemy, cause some nice magic damage and apply slow.
-Depending on the enemy responce, use Blade of the Ruined King's active for more slow, lifesteal and an increase in your speed in order to chase the enemy.
-If the enemy stands for a fight, remember to use your lantern for a shield and Blade of the Ruined King's active to escape if needed.
Thresh's abilities and passive are made for an aggresive playstyle, so try to poke and harass as much as possible. Bait enemies to your tower and execute your combo to bring them under the tower, slow them and do some nice amounts of damage. After Trinity, you can win any 1v1 encounter and feel free to roam or gank mid for a turret.
In case the enemy jungler comes for a gank, use your E to push the enemy away, your ulti for a massive slow or Blade of the Ruined King for an extra speed boost.

Thresh will be dealing both magic damage and physical with his basic attacks. The chances for him to do critical are very high and lifesteal is also a force to be reckoned. The problem is that Thresh uses his abilities for cc and gap closing, while his main damage comes from his basic attacks. A thornmail is an effective way to block his lifesteal by dealing damage back to him with every basic attack he does. Also, champions that use ranged attacks or abilities like Jayce or Cho'gath can poke him easily and stay in a safe distance from his abilities. Champions with hard cc like Garen's silence can ruin your combo, but that is not a considerable threat.

Thresh is a great support, but an even greater offtank. However, in order to use him effectively and crush your enemies, you have to know Thresh's combos and be experienced in both Thresh and top lane. I highly reccomend to learn Thresh by starting as support and when you feel confident, you may move to the top lane. I apologise for any grammatical errors i may have done and feel free to inform me about your arguements, suggestions or further information.