Thresh does not gain armor per level. Instead, Thresh collects the souls of dead enemies by approaching them or by placing Dark Passage's lantern nearby. Each soul permanently grants 0.75 armor and ability power. Champions and large minions and monsters always drop a soul. Small minions and monsters only sometimes drop a soul.
A soul will only drop if the enemy unit dies within 1900 range of Thresh. Souls are visible to allies, and only become visible to enemies if the enemy team has vision of Thresh. Souls disappear if not picked up after 8 seconds.
At level 18, it takes 67 souls (roughly four per level) to surpass Orianna's 62 armor, the lowest innate champion armor. It takes 140 souls (roughly eight per level) to surpass Taric's Shatter-enhanced 116.6 armor, the highest armor possible without the use of items, runes, or masteries.
On Summoner's Rift, the drop rate for souls from small minions is 33%. However, the probability adjusts dynamically. If you are above or below your expected quota of soul drops from small minions, the probability lowers or rises by a small amount until you are back at your quota of drops. It is worth stressing that this only takes into account souls dropped, and not souls collected.
At 255 souls, Thresh gains a new buff, "Soul Gluttony". Soul Gluttony states that he has gained 255 souls as well as how much ability power and armor that is worth. The Damnation buff disappears, and starts again at 1 from your next soul. This will occur each time Thresh obtains 255 souls, with Soul Gluttony updating each time (e.g. 255, 510, 765, and so on).
The number of souls caps at 999,999, at which point Thresh will have 749,999 bonus armor and ability power.
This amount of armor grants Thresh 99.99% damage reduction.
Even with the 35% armor penetration from Last Whisper, this amount of armor grants 99.98% damage reduction.
Active: After a 0.5 second wind-up, Thresh throws out his scythe in a line and forms a tether with the first enemy hit, dealing magic damage and stunning it for 1.5 seconds. Upon hitting an enemy, Death Sentence's current cooldown is reduced by 3 seconds.
While the tether persists, Thresh cannot attack and he will periodically tug on the tether, each time pulling the target a short distance toward himself. After 0.5 seconds, or instantly if he hooks a minion or monster, Thresh can reactivate the ability to use Death Leap.
Spell shields will block the ability and prevent the tether from forming.
Cooldown: 22 / 20.5 / 19 / 17.5 / 16
Cost: 50 / 55 / 60 / 65 / 70 mana
Active: Thresh throws his lantern to the target location where it remains for up to 6 seconds. If an ally right-clicks the lantern, they will pick it up and will be pulled to Thresh's location. If Thresh moves more than ~1500 units away, the lantern will return to him.
For the next 6 seconds, allies who come near the lantern (even while Thresh is holding it) gain a shield that absorbs damage for up to 4 seconds. Allies can only receive the shield once per cast.
The lantern creates a small area of impassible terrain while on the field. Enemies in the area when the lantern is summoned will be nudged to the nearest available space. This is not classified as crowd control (particularly, it will not interrupt channelled abilities).
The lantern's aura radius is ~150 units. This is also the range on the lantern's ability to pick up souls.
The lantern's pick-up radius is not much larger than the model-size of the lantern. However, it is possible to pick-up the lantern through small walls so long as you are within that radius.
The lantern provides vision in a small area for the entire duration.
Thresh cannot click on the lantern himself but he will be shielded if he walks near it.
The lantern can be targeted by Teleport and allied-targeted dashes.
When the lantern is thrown a golden circle is shown displaying the maximum leash range of it.
Thresh can break the leash range returning the lantern to him to instantly shield himself, if he has not been shielded by the ability already.
An ally being carried by Dark Passage will be taken to Thresh's current location, not Thresh's location when the ally grabbed the lantern.
Range: 400 (800 total)
Cost: 60 / 65 / 70 / 75 / 80 mana
Passive: Thresh's basic attacks deal bonus magic damage on each hit. This value is equal to the total number of souls collected, plus a percentage of his attack damage based on the amount of time since his last attack.
Bonus Magic Damage: Souls + up to 80 / 110 / 140 / 170 / 200% AD
Active: Thresh sweeps his chain in a broad line towards a target direction. Enemies hit take magic damage, are knocked in the same direction as the chains, and are slowed afterwards for 1.5 seconds.
Despite its tooltip, the passive bonus damage is based on the amount of time since Thresh's last hit, not his last attack. As the bonus damage does not work against wards or structures, the bonus damage will not reset and will continue to accumulate even while attacking.
Runaan's Hurricane will apply the passive damage to each enemy hit. However, when Thresh strikes one of the enemies the time since his last attack is reset and the other two targets will take only the minimum damage.
When the passive is fully charged the icon of the buff becomes red, Thresh's scythe will glow green and there is a sound effect.
Cooldown: 150 / 140 / 130
Cost: 100 mana
Active: After a 0.75 second delay, Thresh summons 5 spectral walls around him that last up to 5 seconds. Enemy champions that touch a wall take magic damage and are slowed by 99% for 2 seconds, but break the wall. Once one wall is broken, the remaining walls deal half damage and apply half the slow duration. An enemy can be affected by multiple walls.
Magic Damage: 250 / 400 / 550 (+100% AP)
Remaining Walls Damage: 125 / 200 / 275 (+50% AP)
The Box is a point-blank area of effect that creates five walls in a pentagon shape.
Spell shields will block the damage and slow, and that section of the wall will shatter.
Movement speed cannot be reduced below 110, and that slows that would reduce below 220 are modified. To put it another way: a reduction of 99% will not reduce you to 3 movement speed, but rather it will reduce you closer to 110 than a weaker slow would.