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.

Gangplank
Gangplank sheds crowd control effects, then fires a flaming bullet at his target. It deals 210/315/475

magic damage and 33% Wounds the enemy for 8 seconds.Wound: reduces healing received
Gangplank fires a flaming bullet at his target. It deals 230/345/515

magic damage and 33% Wounds the enemy for 8 seconds.Wound: reduces healing received

Lux
Lux sends out a singularity to her current target. When it detonates, it reduces the target's Attack Damage by 40% for 4 seconds, and deals 200/300/450

to nearby enemies. Lux sends out a singularity to her current target. When it detonates, it reduces the target's Attack Damage by 40% for 4 seconds, and deals 220/330/500

to nearby enemies. 
Draven

Gnar

Kai'Sa
Passive: Kai'Sa's attacks apply Plasma. Her next attack against a target with 2 stacks of Plasma deals 110/150/240

magic damage and removes the Plasma.Active: Kai'Sa gains 75% Attack Speed for 10 seconds. This bonus stacks! PASSIVE: Kai'Sa's attacks apply Plasma. Her next attack against a target with 2 stacks of Plasma deals 165/245/405

magic damage and removes the Plasma.ACTIVE: Kai'Sa gains 75% Attack Speed for 10 seconds. This bonus stacks! 
Morgana
PASSIVE: When Morgana deals damage to an enemy, she 40% Sunders and Shreds them for 4 seconds.ACTIVE: Morgana sends out dark bindings towards the 2 closest enemies, dealing 200/300/495 magic damage and stunning them for 1.5 seconds.Shred: reduce Magic Resist
Sunder: reduce Armor
PASSIVE: When Morgana deals damage to an enemy, she 40% Sunders and Shreds them for 4 seconds.ACTIVE: Morgana sends out dark bindings towards the 2 closest enemies, dealing 215/325/535 magic damage and stunning them for 1.5 seconds.Shred: reduce Magic Resist
Sunder: reduce Armor

Vex
Vex launches a blast of gloom at her current target, dealing 240/360/600

magic damage. Every third cast, her gloom becomes unstoppable, passing through enemies and dealing 240/360/600

magic damage to each enemy hit. Vex launches a blast of gloom at her current target, dealing 230/345/570

magic damage. Every third cast, her gloom becomes unstoppable and passes through enemies, dealing 230/345/570

magic damage to the first enemy hit and 150/225/370

magic damage to subsequent enemies hit. 
Bel'Veth

Garen
Garen brings his sword down on the largest group of nearby enemies, dealing 188/282/830

physical damage (160/160/350% of Attack Damage
+ 60/90/200

) to enemies within 2 hexes and stunning them for 1.75/2/6 seconds. Garen brings his sword down on the largest group of nearby enemies, dealing 172/258/785

physical damage (140/140/325% of Attack Damage
+ 60/90/200

) to enemies within 2 hexes and stunning them for 2/2.25/6 seconds. 
Jhin

Neeko
Neeko's frog hops 3 times from enemy to enemy, dealing 75/110/200

magic damage in a small area each time. The final hop is empowered and deals 145/220/600

damage in a large area instead. Neeko's frog hops 3 times from enemy to enemy, dealing 75/110/300

magic damage in a small area each time. The final hop is empowered and deals 150/225/700

damage in a large area instead. 
Samira

Twisted Fate
Twisted Fate draws 6/6/12 cards and begins drawing another card after every auto attack. After 2.5 seconds, Twisted Fate throws all of his drawn cards, each dealing 60/95/350

magic damage. The final card thrown is a red card that deals 200/300/900

magic damage to nearby enemies. Twisted Fate draws 6/6/12 cards and begins drawing another card after every auto attack. After 2.5 seconds, Twisted Fate throws all of his drawn cards, each dealing 55/85/250

magic damage. The final card thrown is a red card that deals 190/285/800

magic damage to nearby enemies. 
Warwick
PASSIVE: Warwick gains 20%/20%/50%

Omnivamp. Upon his first takedown, he enters KILL MODE 2.0, granting himself 60% Attack Speed and causing him to leap to new targets for the rest of combat.ACTIVE: Warwick attacks his target 6 times, dealing a total of 322/504/1890

physical damage. (460/480/1200% Attack Damage). If his target dies he gains 10 mana for each remaining slash. PASSIVE: Warwick gains 20%/20%/50%

Omnivamp. Upon his first takedown, he enters KILL MODE 2.0, granting himself 60% Attack Speed and causing him to leap to new targets for the rest of combat.ACTIVE: Warwick attacks his target 6 times, dealing a total of 322/504/1890

physical damage. (460/480/1200% Attack Damage). If his target dies he gains 10 mana for each remaining slash. 
Fiddlesticks
Fiddlesticks teleports into the largest cluster of enemies and fears them for 1/1/5 seconds. For the next 5/5/30 seconds, Fiddlesticks drains the life from nearby enemies dealing 85/130/800

magic damage per second and healing for 20% of the damage dealt. Fiddlesticks teleports into the largest cluster of enemies and fears them for 1/1/5 seconds. For the next 5/5/30 seconds, Fiddlesticks drains the life from nearby enemies dealing 90/135/800

magic damage per second and healing for 20% of the damage dealt. 
Nunu & Willump
Passive: Nunu and Willump roll a ball around the arena towards the furthest enemy. The ball deals 120/180/2000

magic damage to all enemies it passes through. When they reach their target, they will find a new destination. Nunu and Willump gain 30/30/90 Mana per second.Active: Nunu and Willump grow the ball, increasing their movement speed, the size of the ball, and the amount of damage by 40%. PASSIVE: Nunu and Willump roll a ball around the arena towards the furthest enemy. The ball deals 120/180/2000

magic damage and briefly stuns all enemies it passes through. When they reach their target, they will find a new destination. Nunu and Willump gain 30/30/90 Mana per second.ACTIVE: Nunu and Willump grow the ball, increasing their movement speed, the size of the ball, and the amount of damage by 40%. 
Syndra
Syndra grants a 200/600/4000

Health shield to a random champion on your bench, then flings them into the arena inside an orb at her closest enemy. The orb deals 250/375/2500

magic damage to enemies hit. Traits of champions flung onto the board do not become active, except for Corrupted.
Syndra grants a 200/600/4000

Health shield to a random champion on your bench, then flings them into the arena inside an orb at her closest enemy. The orb deals 250/375/2500

magic damage and briefly knocks up all enemies hit. Traits of champions flung onto the board do not become active, except for Corrupted.

Ultimate Ezreal

Urgot

Gadgeteen
(3) Create 1 item, 3% per item.
(5) Create 2 items, 9% per item.
(3) Create 1 item, 3% per item.
(5) Create 2 items, 10% per item.

Hacker
(2) +20% Omnivamp
(3) +30% Omnivamp for Hackers, +10% for the rider
(4) +40% Omnivamp for Hackers, +20% for the rider
(5) +50% Omnivamp for Hackers, +30% for the rider
(3) +30% Omnivamp for Hackers, +10% for the rider
(4) +40% Omnivamp for Hackers, +20% for the rider
(5) +50% Omnivamp for Hackers, +30% for the rider

InfiniTeam
(3) 1 portal opens, 40% damage and 40% HP
(5) 2 portals open, 55% damage and 55% HP
(7) 2 portals open, 90% damage and 90% HP
(3) 1 portal opens, 50% damage and 50% HP
(5) 2 portals open, 60% damage and 60% HP
(7) 2 portals open, 95% damage and 95% HP

LaserCorps
When a LaserCorp drone pilot attacks or is hit by an attack, their combat drone deals magic damage to the agent's target (0.40 second cooldown). When a unit with a drone dies, the drone is reassigned to another unit with a drone.Drone lasers deal:(3) 30 magic damage
(4) 50 magic damage
(5) 60 magic damage. All champions get a LaserCorp drone.
(6) 90 magic damage. All champions get a LaserCorp drone.
When a LaserCorp agent attacks or is hit by an attack, their drone deals magic damage to the agent's target (0.40 second cooldown). Drones are reassigned to another champion with a drone when the agent dies.

Mascot
Your team heals a percentage of their maximum Health every 2 seconds, and Mascots heal double the amount.When Mascots die, they retreat to the sidelines to cheer on your team. Your team's healing increases by 1.50% for each cheering Mascot. Your team heals a percentage of their maximum Health every 2 seconds, and Mascots heal double the amount.When Mascots die, they retreat to the sidelines to cheer on your team. Your team's healing increases by 1% for each cheering Mascot. 
Parallel
Ultimate Ezreal's Ability summons one additional temporal duplicate.
Ultimate Ezreal's Ability summons two additional temporal duplicates.

Prankster
(2) Once per combat at 50% Health, Pranksters spawn a target dummy, move to a safe location, and restore 150 Health.
(3) And, Prankster dummies stun the enemy that killed them for 1.50 seconds.
(4) The Health restore is increased to 250 Health and the stun duration becomes 2 seconds.
(2) Once per combat at 50% Health, Pranksters spawn a target dummy, move to a safe location, and restore 150 Health.
(3) And, Prankster dummies stun the enemy that killed them for 1.50 seconds.
(4) The Health restore is increased to 350 Health and the stun duration becomes 2 seconds.

Quickdraw
(2) 55% total damage.
(3) 120% total damage.
(4) 185% total damage.
(2) 70% total damage.
(3) 140% total damage.
(4) 220% total damage.

Renegade
(3) 25% bonus damage, extra 20% for last alive
(5) 40% bonus damage, extra 25% for last alive
(7) 65% bonus damage, extra 35% for last alive
(3) 25% bonus damage, extra 20% for last alive
(5) 40% bonus damage, extra 30% for last alive
(7) 70% bonus damage, extra 40% for last alive

Sureshot
(2) +6% Attack Damage
(3) +11% Attack Damage
(4) +16% Attack Damage
(5) +24% Attack Damage
(2) +7% Attack Damage
(3) +12% Attack Damage
(4) +18% Attack Damage
(5) +25% Attack Damage