Datamined changes from current PBE release. Be aware that these changes are tentative and they might be changed or even reverted prior to the live patch.
Datamining only captures numerical changes. It doesn't capture changes to mechanics and bugfixes that may also significantly affect balance.
Due to the nature of how the datamining works it may also includes some of the changes that are already added to the live version in the most recent patch.
Updated: Mar 25 8AM

Anivia
Fire an ice shard at target that deals 325/455/650 (
) magic damage. If they are Chilled, the damage Critically Strikes.
Damage: 455 (
) [325/455/650]
Fire an ice shard at target that deals 355/530/750 (
) magic damage. If they are Chilled, the damage Critically Strikes.
Damage: 530 (
) [355/530/750]

Blitzcrank

Jhin

Lulu
Deal 330/500/750 (
) magic damage to target and make them dance for 2 seconds. The projectile then bounces to the nearest target, dealing 140/210/315 (
) magic damage. Deal 330/500/750 (
) magic damage to target and make them dance for 1 seconds. The projectile then bounces to the nearest target, dealing 140/210/315 (
) magic damage. 
Shen

Cho'Gath
Restore 200/225/400 (
) Health and rupture a 2 hex circle beneath target. After a brief delay, enemies within are knocked up for 1.5 seconds and take 88/152/248 (
) magic damage. Gain 10/15/25 permanent max Health (Total: @TFTUnitProperty.:TFT16_ChoGath_BonusHealth@). Restore 200/225/400 (
) Health and rupture a 2 hex circle beneath target. After a brief delay, enemies within are knocked up for 1.5 seconds and take 88/152/248 (
) magic damage.
Permanent Health
[10/15/25]

Rek'Sai
Dash around target and snip 5 (
) times, dealing 50/75/120 (
) magic damage to them and 25/35/60 (
) damage to all other enemies in a cone. 
Malzahar

Milio

Vayne
Damage: 190 (
) [125/190/600]
Damage: 210 (
) [140/210/600]
Damage Per Second: 18 (
) [8/18/160]
Damage Per Second: 26 (
) [13/26/160]
Passive: All allies gain 10/20/100 Armor.Active: Gain 750/950/3000 (
) Shield for 4 seconds. Impale up to three nearby enemies in a line, dealing 84/126/1750 (
) physical damage and Stunning them for 1.5/1.75/8 seconds.
Passive: All allies gain 15/30/100 Armor.Active: Gain 750/950/3000 (
) Shield for 4 seconds. Impale up to three nearby enemies in a line, dealing 84/126/1750 (
) physical damage and Stunning them for 1.5/1.75/8 seconds.

Taric
Passive Magic Resist
[10/20/100]
Passive Magic Resist
[15/30/100]
Passive: For every 250 ability damage dealt to enemies in player combat, gain Stardust. Stardust makes The Skies Descend more powerful. Active: Crash a star on target, dealing 525/725/5000 (
) magic damage in a 2 hex radius.Stardust Upgrades:25: Create a shockwave that deals 100/150/1000 (
) additional magic damage in a 3 Hex radius.60: The star crash deals 15% more damage.140: Shockwave increases to a 4 hex radius.200: Knock up targets in the star crash for 1.5 seconds.300: Shockwave increases to 10 radius.550: The star crash deals 33% bonus true damage.800: Also call down a meteor storm that deals 500/750/9999 (
) magic damage split between living enemies.1444: Summon a black hole at the epicenter, instantly killing enemies within.
Damage: 725 (
) [525/725/5000]
Passive: For every 250 ability damage dealt to enemies in player combat, gain Stardust. Stardust makes The Skies Descend more powerful. Active: Crash a star on target, dealing 475/700/5000 (
) magic damage in a 2 hex radius.Stardust Upgrades:25: Create a shockwave that deals 100/150/1000 (
) additional magic damage in a 3 Hex radius.60: The star crash deals 15% more damage.140: Shockwave increases to a 4 hex radius.200: Knock up targets in the star crash for 1.5 seconds.300: Shockwave increases to 10 radius.550: The star crash deals 33% bonus true damage.800: Also call down a meteor storm that deals 500/750/9999 (
) magic damage split between living enemies.1444: Summon a black hole at the epicenter, instantly killing enemies within.
Damage: 700 (
) [475/700/5000]
Damage: 
[20/30/200]
Damage: 165 = 135 (
) + 30 (
) [90/135/1500]
Secondary Damage: 66 = 40% of 165
Slam Circle Damage: 330 = 200% of 165
Damage: 
[15/25/200]
Damage: 160 = 135 (
) + 25 (
) [90/135/1500]
Secondary Damage: 64 = 40% of 160
Slam Circle Damage: 320 = 200% of 160

Chronokeeper
Every 2 casts, the Chronokeeper stores 1 XP. If he has enough stored for you to level up, he transfers you the required XP. If you are level 10, he instead gains 15% Damage Amp.Stored XP: 0<ShowIfCustom.Set=TFTSetEventCT>In Choncc's Treasure, the amount of casts required to gain XP is increased to 3 until Stage 3-5.</ShowIfCustom.Set=TFTSetEventCT> Every 2 casts, the Chronokeeper stores 2 XP. If he has enough stored for you to level up, he transfers you the required XP. If you are level 10, he instead gains 15% Damage Amp.Stored XP: 0<ShowIfCustom.Set=TFTSetEventCT>In Choncc's Treasure, the amount of casts required to gain XP is increased to 3 until Stage 3-5.</ShowIfCustom.Set=TFTSetEventCT> 
Darkin
(1) Darkin gain 15% Omnivamp.
(2) AND you heal for 25% of the player damage you deal.
(3) AND whenever Darkin restore 600 Health, they deal 333 magic damage to the 2 closest enemies.
(1) Darkin gain 15% Omnivamp.
(2) AND you heal for 25% of the player damage you deal.
(3) AND whenever Darkin restore 525 Health, they deal 400 magic damage to the 2 closest enemies.

Gunslinger
Gunslingers gain Attack Damage. Every 4th attack from Gunslingers deals bonus physical damage.(2) 22%
, 100 bonus damage (4) 40%
, 200 bonus damage Gunslingers gain Attack Damage. Every 4th attack from Gunslingers deals bonus physical damage.(2) 22%
, 100 bonus damage (4) 44%
, 200 bonus damage 
Yordle
(2) Yordles gain 40 Health and 5% Attack Speed for each unique Yordle fielded. 3 star Yordles grant 100% more!
(4) AND your first shop each round has a Yordle in it!
(6) AND get 1 free rerolls each round!
(8) AND get a Yordle Grab Bag each round!
(2) Yordles gain 40 Health and 5% Attack Speed for each unique Yordle fielded. 3 star Yordles grant 120% more!
(4) AND your first shop each round has a Yordle in it!
(6) AND get 1 free rerolls each round!
(8) AND get a Yordle Grab Bag each round!

Trials of Twilight
Gain 2 Xin Zhao. Your strongest Xin Zhao constantly strikes nearby enemies and executes enemies. After 5 player combats as a 3-star, unlock Zaahen. He replaces Xin Zhao and takes his items.
Gain 2 Xin Zhao. Your strongest Xin Zhao constantly strikes nearby enemies and executes enemies. After 2 player combats as a 3-star, unlock Zaahen. He replaces Xin Zhao and takes his items.

Trials of Twilight II
Gain 1 Xin Zhao and a Bloodthirster. Xin Zhao becomes an Attack Fighter. After 5 player combats as a 3-star, unlock Zaahen. At the start of the next 2 stages, gain a Lesser Champion Duplicator. Gain 1 Xin Zhao and a Bloodthirster. Xin Zhao becomes an Attack Fighter. After 2 player combats as a 3-star, unlock Zaahen. At the start of the next 2 stages, gain a Lesser Champion Duplicator.