New season
With the new season comes more focus on objectives which makes roaming ability more important than before. For this reason I'm taking Boots of Swiftness and Trailblazer more than before. You also want to try to play for first tower as well so I'm currently taking Demolish instead of Font of Life to get more damage on towers during roams to try and secure the Feats of Strengths more easily for my team.

Sixth Sense seem to be terrible options because of the long CD.
Grisly Mementos seem like an ok option as it gives your Oracle Lens a very short CD.
Deep Ward may be the best option as they are more annoying for the enemy to clear them now and stay around for a little while longer. Ultimately I think this was a large nerf to the Domination tree, but if you really love Relentless Hunter I'd recommend taking Deep Ward.


Abyssal Mask gives slightly better stats, but will be less effective against MR stacking, think of it as Flat Magic pen instead of Percent Magic pen. Still good if you only have one source of AP dmg and enemies aren't building MR.


Swiftmarch is going to be the option in general for the %MS boost we get which scales of off our Total MS as opposed to our Bonus MS like most other items.
Forever Forward also gives the Total MS speed, but are less useful in combat.
Chainlaced Crushers and Armored Advance are good options if against their respective damage type.
Crimson Lucidity are good boots as they increase your haste by a fair amount, but the passive feels a bit weird on Thresh. Still very strong boots though. (Note that these boots are currently bugged on live servers where they only give a 0.3 seconds reduction on Flash cooldown as opposed to the intended 28 second reduction.)

PROS + Very strong early + Good engage and disengage tools + You will have a lot of agency + Very fun to play Thresh has always been present in the support meta and the reason for this is that his kit is flexible and allows multiple different playstyles. If you want to play a support champion that can save teammates, lock down single targets very effectively or control multiple enemies with a 5-man Flay then you should consider learning to play Thresh.

CONS - Very skill dependant - Will struggle with weak adc - Has no sustain - Gets outscaled by enchanters Thresh has a very high skill ceiling. This means that you will need to spend a lot of time learning his kit to be able to pilot him effectively. You also have no sustain in lane so if you're playing against a long range lane it can be difficult to get any action going in the botlane especially if you can't access the bushes.

In this chapter I'll go over a few build examples and when to go for them. You don't have to follow a single option and can mix and match as these are only suggestions despite having good synergies in each build.

Early roam aggression:
This build will be for you who want to have an easier time roaming across the map and affecting every lane with your early game presence.
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Works best if your Adc isn't going to be in too much danger if you leave the lane for an extended amount of time or if the enemy Support will be roaming as much as you.
Choosing between the two boot options is mostly a personal choice. I prefer to take Boots of Swiftness, but if you reset with only 600G and the enemy doesn't have many slows you can take Synchronized Souls instead.
Because of the lack of Haste in this build you can take Precision second to get Legend: Haste to get more BASIC Haste.
Alternatively you can go Domination to get even more MS from Relentless Hunter.


Warden:
This build is probably the most standard build for Thresh as it works into just about anything and is never bad.

These are the two main pieces that will help you peel for your entire team and give a little extra to one specific carry. You can obviously swap the order if you don't need any MR from Locket of the Iron Solari early or if the enemy has mostly single target damage focused onto your ADC then Knight's Vow would be better first. Frozen Heart is really good against most AD champions that'll dive your backline and still helps against a lot of ranged champions as well.


Front-to-back:
This build is more focused on full teamfight supporting rather than peeling for one specific hard carry and is probably my favourite build.

It works best when the fights are going to be slower front-to-back fights where you'll have an easier time using your Redemption without your teammates needing to run away. Revitalize synergizes really well with this setup and Guardian adds even more value. If you need more MR later in the game Spirit Visage makes all the healing and shielding you give yourself more valuable.

GUARDIAN Great into most matchups.

AFTERSHOCK Necessary against engage support.

GLACIAL AUGMENT Fine vs double ranged or dive.

Guardian is great against most matchups as you can fairly easily decide when to proc it as you're ranged and can more easily space with your Adc so it won't get wasted, you can also proc it with your Dark Passage from range. Aftershock is necessary against engage matchups such as Leona or Nautilus as it will allow you to facetank their engage and create space for your Adc. It will also help in later fights to make sure you don't get oneshot as easily. If you're the only tank/frontline on your team you need it even more. Glacial Augment helps in double ranged matchups as you make it harder for them to run away from you when you engage on them and also against dive comps as it will make it easier for your carries to kite them when the divers are slowed.

RESOLVE

Guardian is really effective as it will help you protect a single teammate more and you can easily use it with your Dark Passage from long range. Aftershock makes you tankier after you immobilize an opponent, which will allow you to buy more space in front of your team or more easily survive in lane vs another engage support.

Currently I think Demolish will be the better choice as they can help you take first tower faster which might make it easier to get the Feats of Strength. Whenever you roam try to push out the wave and get a Demolish proc on the tower without putting yourself at too much risk or taking too much time. Font of Life is still the same as before, not great (especially on ranged champions like Thresh), but still a fine choice.

Generally Second Wind is going to be the better option as it will always give you extra sustain and value while Bone Plating can be wasted by random poke like Volley for example. So if you need to go Bone Plating due to the early game trading be mindful of not wasting it.

Overgrowth gives you a considerable amount of health in the late game. Revitalize is actually really good if you like going Guardian and Locket of the Iron Solari into Redemption.

INSPIRATION

Hextech Flashtraption is also a good option for catching your enemies off guard. Cosmic Insight gives you summoner spell haste which allows for more aggression. Biscuit Delivery can give you some free healing and max HP which will help against more aggressive early games.

INSPIRATION

Glacial Augment allows you to catch people even easier thanks to the slow and it also works really well defensively as it reduces damage to your teammates by 15% from those affected.

Hextech Flashtraption can catch your enemy off guard and lead to more picks. Stay out of vision while channeling it like in a bush or behind a wall.

Biscuit Delivery will keep you healthier for free and gives you extra max HP. Use when you're low for more value.

Cosmic Insight will give your summoner spells more haste which will enable more aggression.

RESOLVE

First you have to choose either Second Wind or Bone Plating depending if you're up against poke or engage in lane. (Stay mindful of not wasting Bone Plating from ADC poke damage.) Then Overgrowth is going to be better choice in general, but Revitalize is fine if you're planning on going both Locket of the Iron Solari and Redemption. It also slightly increases the slow from Glacial Augment.

Rune Shards

I always take Ability Haste in the top row because Thresh scales so well with Haste, but if you want to fight early and put an extra point or two into Flay then the extra AD from Adaptive Force can be quite useful.

Most often I will go for the Health Scaling to get tankier, but if I want to go for more roaming with Trailblazer I will take Movement Speed instead.

The last row is going to depend on your early lane. If you need the early health against an engage Support or and aggressive ADC you want the Flat Health to help survive the early fights, but if you're facing more scaling and an enchanter Support then you can be greedier and take the Health Scaling.

These secondary rune options are more niche and not something I would recommend to someone just trying out Thresh, but if you have more experience and want to try something new and exciting these runes are good situational options.

PRECISION

Legend: Haste quite quickly gives you a lot of extra Haste to compensate for some builds where you don't get any Haste from the items. Triumph is the only other rune you can take in this tree and it does give some nice healing and extra gold income.

DOMINATION

Relentless Hunter eventually gives you a lot of extra MS to roam around the map and quickly impact other lanes and coming back to protect your ADC. Deep Ward is your other option in this tree, it gives your deep wards extra health and duration, making them more annoying to deal with for the enemy.

Great defensive item Locket of the Iron solari is still a fantastic item that helps you protect your teammates. This is just a fantastic item that should always be at the back of your mind.

Chivalry isn't dead Knight's Vow is tailor-made for Thresh, it gives you great stats for the cost and helps you peel for your fed teammate and keep them alive (and get some healing for yourself as well).

Speedy roams Trailblazer is a good item that gives you and your teammates movespeed to cross the map faster.

Stickiness Zeke's Convergence creates a slowing field around you which makes you sticker and harder to kite away from.

Big teamfight heal Redemption is a great teamfight item, it helps in keeping your entire team alive during a fight. Don't be afraid of using it before a fight if you're about to take an objective.

Anti-Attack Speed Armor, haste and even mana are all good stats on him and the added benefits of the passives make this a really compelling item when facing multple AD or AA based champions.

Anti-healing Thornmail has been shrunken down so it's now more viable to buy as a support. Gives a decent amount of stats for the cost as well as Grievous Wounds. You should wait until 3rd or 4th item to upgrade Bramble vest into Thornmail.

Anti-Crit Gives good stats, but a bit expensive. Take less damage from crits, but most importantly has a big slow effect to either catch people or help your teammates kite more easily.

Aggressive MR Abyssal mask makes your AP damage dealers do more damage to enemies close to you. So it's a more aggressive MR item than Spirit Visage.

Defensive MR Spirit Visage gives you more defensive stats than Abyssal Mask, and makes shields and heals more effective on yourself.

Expensive MR Kaenic Rookern is a more expensive option for if you're winning and have the extra money to spend and also if you don't have any AP damage to amplify from your teammates.

Anti hard CC item Mikael's Blessing gives you more oppurtunities to peel your team if the enemy has some hard hitting CC spells e.g Enchanted Crystal Arrow or Sleepy Trouble Bubble.

Great objective vision control Vigilant Wardstone should always be your final item if you get this far. It gives you more wards on the map, more control wards in your inventory and some nice bonus stats as well.

Passive: Damnation Full Ability Description Innate: Thresh's armor does not increase through growth (per level). Innate: Champions, large minions and large monsters that die near Thresh drop a Soul for 8 seconds. Epic monsters drop 2 Souls while lesser minions and monsters have a 33.3% chance to drop a Soul. Thresh automatically collects Souls near him or a placed Dark Passage. Soul: For each stack, Thresh gains 1 ability power and 1 bonus armor. Thresh doesn't gain any Armor per level, in return enemies dying near him periodically drop souls for him to pick up each giving him 1 AP and 1 Armor. General tips ✦Each soul has a gold value of 40 gold so don't underestimate them. ✦You can use your Dark Passage to pick up souls from a safe distance, beware of wasting the CD if you might get ganked though. Q: Death Sentence Full Ability Description Active: Thresh throws out his scythe in the target direction, becoming unable to move or attack while it is in flight. The scythe catches the first enemy hit to deal magic damage, stun and reveal them for 1.5 seconds, as well as reduce Death Sentence's current cooldown by 2 seconds. Thresh will also mark the target Shackled for 1.5 seconds, during which he is unable to declare basic attacks, and is slowed by 20% for 1 second. While the target is stunned, Thresh tugs twice over 0.8 seconds, pulling the target a short distance with each tug. After 0.5 seconds of hitting an enemy or instantly after hitting a minion or monster, Thresh can recast the ability while the target is Shackled, which will cause him to stop tugging. Recast - Deathly Leap: Thresh dashes to the Shackled enemy, becoming able to attack again upon arrival. He can cast Dark Passage and Flay during the dash. Thresh's most iconic spell, the hook. Used for making picks and peeling threats off of your carries. Lowers the cooldown whenever you hit an enemy. When you hit an enemy you tug them in twice before letting them go, but you can recast your Death Sentence to dash towards them instead. General tips ✦If your enemy has Cleanse you should hold your Ignite until after they Cleanse your Death Sentence. This way they don't Cleanse two things at once. ✦Try to pay attention to where the enemy wants to dodge and try to learn the dodging patterns of your enemies. If you notice that the enemy Adc doesn't dodge, but the Support dodges to the left keep that in mind for when you aim the skillshot. W: Dark Passage Full Ability Description Active: Thresh throws his lantern to the target location over 0.5 seconds, lasting for 6 seconds while he remains nearby and granting sight of its surroundings. If Thresh moves too far away from the lantern, it returns back to him immediately. Thresh and the first allied champion to come near the lantern are granted a shield for 4 seconds. An ally can select the lantern while in proximity of it, dashing to Thresh and gaining the shield. An ally cannot select the lantern while immobilized, grounded, or silenced. The lantern will not expire from Thresh moving too far away if he is dashing with Deathly Leap. Probably Thresh's most powerful spell. Can be used to very easily reposition your teammates either for the purposes of peel or for followup on your engage. Also gives a shield that scales off of your souls from Damnation. General tips ✦Place the Dark Passage in the direction your teammate is running. This makes it easier for them to click it and harder for the enemy to block it with a ward. ✦You can use your Dark Passage to check bushes or over walls instead of facechecking. ✦Your Guardian will be active on a teammate when you shield them with Dark Passage from range. E: Flay Full Ability Description Passive: Thresh's basic attacks are empowered to deal bonus magic damage, with the AD ratio increasing over 10 seconds without basic attacking enemies. Active: Thresh sweeps his chain across the ground in a broad line and a radius around him, starting behind him and towards the target direction. Enemies hit are dealt magic damage and knocked 200 units in the target direction, and then are slowed for 1 second. An incredible tool that will separate the good Thresh players and the great ones. Can be used as a simple knockback for peel or to lock people down for longer or you can utilize it further by cancelling dashes such as Rocket Jump or Elastic Slingshot. It also has a passive that makes your AAs deal more magic damage based on your souls and total AD. General tips ✦If you're playing against a short range botlane you can put one or two more points into Flay and maybe take an extra Adaptive Force so your AA will do some more damage. ✦Hold your Flay for just after your Death Sentence ends against certain champions like Kha'Zix, this way you are more likely to cancel their escape ability which they are most likely spamming while they're CCed. R: The Box Full Ability Description Active: Thresh erects a pentagon of spectral walls around him that each last for 5 seconds. A wall will break upon enemy champion contact, dealing magic damage and slowing them by 99% for 2 seconds. Enemies that break a wall cannot do so again for 1 second. Subsequent walls they break will deal no damage and slow for only 1 second. Thresh summons a pentagon which damages and slows the first enemy hit. Subsequent enemies just gets slowed for half of the duration instead. Can be used to either help burst a squishy target during your CC or to dissuade the enemy from chasing you further. General tips ✦After you hit a Death Sentence you can immediately cast The Box during the CC and then Flay the enemy into one of the walls for a massive slow and a decent chunk of damage on a squishy target.

Warding is an important skill for any support player to master, but even more so for a support like Thresh where you thrive in the fog of war, catching enemies when they are unaware of your presence as they're trying to rotate from one lane to another.
These ward maps will help you place wards that will be effective in most games, but do note that when against certain junglers or laners you will need different wards. For example a Zac can gank you from further away over walls while a Shaco can gank over walls while being stealthed. Against these junglers consider placing deeper wards (if it's safe to do so) to spot them when they're clearing their jungle camps.

Early game wards for blue and red side
Mid game wards for mid and river control
Late game wards for objectives
Ward placements
These specific ward spots can take some practice to get them right so I would recommend that you do some "ward drills" in a Practice tool game until you can place them consistently. If you're struggling with the consistency do these drills before you queue up for your games that day as a sort of warm-up. Make sure to have indicators enabled to more easily see where the ward will get placed.

This chapter will have random information and tips regarding that didn't fit into the guide elsewhere.

Runes:

Taking Revitalize may look odd on Thresh as he only has a weak shield on his Dark Passage, but it will also buff your Guardian, Font of Life, Second Wind, Locket of the Iron Solari and your Redemption. The small 5% heal and shield power (+10% extra on targets below 40% HP) may not look like a lot but it will add up over the course of a game.

Assuming you don't miss a single minion death then Overgrowth will give you the 3.5% bonus max HP on the wave that arrives in lane at 10:30. At that point the other part of Overgrowth gives you 45 HP. At this point Damnation will have dropped around 42 Souls giving you 42 armor and AP. Needless to say that in a real game you will be missing some minions either from roaming, recalling or being forced off the wave so realistically this rune will take longer to fully come online.

Health Scaling vs Flat Health in the bottom row of rune shards? Generally scaling shards are worse on supports as we get less XP than other roles and we need to fight early especially on Thresh. So I would recommend taking Flat Health. Against some scaling matchups however you can be greedy and take the Health Scaling.
If you really need tenacity you're better off just buying Mercury's Treads instead of taking the Tenacity and Slow Resist rune shard in my opinion.

Cosmic Insight lowers the cooldown of Flash by 56 seconds which will give you a large window where you will have it up and the enemy wont if you both use Flash at the same time.
Going Ionian Boots of Lucidity in addition with Cosmic Insight lowers the cooldown by 69 seconds instead. nice

Legend: Haste actually gives you BASIC ABILITY Haste. This means that it won't affect your ultimate abilty. On Thresh this is kind of irrelevant.
What does matter though is that the Haste that you get from Legend: Haste will not show up in your stats tab next to your portrait in game, so it will look like you have less Haste than you actually have.
Even though it doesn't show up in your stats it still affects your cooldowns of your basic abilities.

Thresh's Adaptive Type is AD and will not change to AP no matter how many souls he gets from Damnation. The only way to change Adaptive Force from AD to AP is by buying an item that has AP like for example Shurelya's Battlesong.


Items:

The damage taken from Knight's Vow deactivates your Synchronized Souls and cancels your recall even if the damage is only from minions.

When in a fight without your Knight's Vow target (whether they're dead or just not in the fight) you should try to change your mark to another teammate. This way you're still getting value from the passive. Another thing to remember is that the target doesn't have to be your adc. If your adc is super behind while your midlaner is smurfing you should change priorities. Don't get stuck in the mindset of having to support only your adc!

Solstice Sleigh is not a heal it only gives bonus HP, so it is not affected by grievous wounds or heal & shield power. Think of it as a mini Wild Growth.

If you finish your support quest and are starting to have regrets over your choice of item (whether you missclicked the wrong item or think another item will have more value) you can sell your Solstice Sleigh and buy Celestial Opposition from the shop. This does cost you 240 gold because you only get 160 gold from selling it and then you have to pay 400 gold to buy it again so it's not super ideal, but it is good to know for those awkward times when you accidentally click the wrong one or get into a really long game. Generally I'd say that Solstice Sleigh gets outscaled by Celestial Opposition.
Selling and rebuying your support item does NOT remove the wards that you have placed on the map.

Spirit Visage increases all the shielding and healing you receive by 25%, this includes everything you give yourself as well, for example Dark Passage, Locket of the Iron Solari and Guardian.
The healing you receive from fountain also gets increased by Spirit Visage and also gets tracked so don't trust the healing number when you hover over it in game.


Abilities:

Generally starting with Flay is best as it gives you more power and allows for both proactive trades and defensive peel, however when playing against a double ranged botlane I like starting Death Sentence as it gives me the opportunity to catch the enemy off guard level 1.

When you hit a Death Sentence on someone don't immediately use Flay. Instead wait for your Death Sentence to tug them in twice and then Flay them right after your Death Sentence ends. This way you can CC them for longer and potentially cancel their dash/jump with your Flay. Most people will be spamming their escape button during your Death Sentence so this way you will be more likely to cancel their Rocket Jump for example. If you're struggling with the timing then spend a few minutes in Practice Tool and you can get it down pretty fast.

I've made other guides as well, but I don't update them as often as this one. Check them out if you'd like!

Embrace the depths
Warm hugs for everybody!

If you have any questions or criticisms please leave them in the comment section, I'd gladly answer any question you have!

Special thanks to jhoijhoi for their great guide to coding.