Thanos by Slombeeper

Thanos's abilities are weak, he must complete quests to increase his power through the infinity stones. Each completed quest grants a stone with a powerful effect. For each stone Thanos has, he gains 7% additional maximum health, stacking up to 6 times. Upon gathering all infinity stones, gain 8% additional maximum health. Dying causes Thanos to lose one random stone he has collected.

Time Stone
Quest: Hit enemy heroes with 40 basic attacks.
Reward: Activate to reverse time in an area after 3 seconds, causing all heroes to be returned to their position they were and setting all heroes' health to the same it was when this ability was cast. Ability cooldowns are not affected by this. Passive: Reduce your respawn time by 25%.

Space Stone
Quest: Successfully channel Recruit 8 times.
Reward: Activate to open a vortex to anywhere on the battlefield, you and your allies can enter it. 2 seconds after entering the vortex, you are teleported to its exit. Passive: Increase your mana generation by 50%.

Soul Stone
Quest: Kill 50 minions.
Reward: If an ally hero is killed by an enemy hero, the enemy is marked for 2 seconds. Activate this ability when near that enemy to instantly kill them. Passive: Increase all non-heroic healing recieved by 50% and your health regeneration by 100%.

Reality Stone
Quest: Collect 15 regeneration globes.
Reward: Activate on a boss or mercenary camp to make it appear captured and travel down a lane. The boss or mercenary illusion has 1 health but deals damage. Self-cast to summon an illusion of Thanos. Passive: When Thanos Hearthstones or self-casts Reality Stone, he creates an illusion of him that continues to do whatever he was doing for 20 seconds. Illusion deals 50% less damage and has 30% less health. Only 1 illusion may be active.

Power Stone
Quest: Kill 4 enemy heroes.
Reward: Activate to increase the passive effects of all gems by 50% for 10 seconds and cause every third basic attack to deal 150% of its damage in an area. Passive: Deal 20% bonus damage and gain 10 armor.

Mind Stone
Quest: Hit 20 enemy heroes with abilities.
Reward: Activate to grant all allies heroes 25 armor for 3 seconds. Passive: Each nearby enemy hero reduces the cooldown of all basic abilities by 12%. Up to 4 times.

Mana: 50
Cooldown: 10 seconds
After 0.5 seconds, deal 270 damage to an enemy and stun them for 0.75 seconds.

Mana: 70
Cooldown: 18 seconds
Heal yourself for 20% of your maximum health. Enemy hero deaths resets this ability's cooldown.

Mana: 45
Cooldown: 8 seconds
Leap a short distance and slow enemies in an area by 30% for 1 second.

Mana: 100
Cooldown: 90 seconds
Become unstoppable and channel a short beam after 0.5 seconds dealing 1060 damage over 3 seconds that knocks enemies back. Deals 5% more damage for each Infinity Stone collected.

Mana: 120
Cooldown: 120 seconds
Channel for 2 seconds, then kill all minions and deal 40% of the maximum health of heroes and mercenaries on the enemy's side of the map. Also damages allies.

Can only be used if Thanos has all the infinity stones