Name of hero: Narud
This hero can copy any abilities of any hero. When you start game, first used basic abilities (QWE) make copy from picked hero. If you press Q and pick Li-Ming, you can use Magic Missiles on Q. And so on. But it works only once. After copying, you can use this skill to end the game.
Combat Trait: Immortality - when the hero gets the fatal damage, it does not die, and teleports to their base. This has the effect cooldown 180 seconds.
Below I'll show exemplary talents that could have Narud. These talents just as an example, and there is no balance. Just an idea.
1 level
Increasing the range of skills by 20% (Q)
Reduces the mana cost by 25% (W)
Reduces the cooldown by 10% (E)
Collecting Regeneration Globes permanently increases Mana Regeneration by 0.10 per second.
4 level
Increases movement speed by 30% for 2 seconds (W)
The basic attacks deal 20% additional
First Aid
Advanced block
7 level
Battle Momentum
It gives cloak 1 second. It increases the mana cost by 15%. (Q)
Slows target by 20% (W)
Reduced cooldown to 20 seconds (Trait)
10 level
Great Copy - copies the selected hero heroic ability at first time.
Creations Power - increases the effectiveness of basic skills by 50%.
13 level
Giant Killer
Reduced cooldown to 20 seconds (Trait)
It increases the scope of the ability by 30% (Q)
Spell Shield
16 level
It increases the scope of the ability by 30% (E)
Does not require skill mana costs, but increases to 20% cooldown. (Q)
Reduced cooldown to 20 seconds (Trait)
Blood for Blood
20 level
A masterful creation. It increases the capacity by 100%. (Creations Power)
Grandmaster copies. Copies the main heroic ability of this skill level 20. (Great Copy)
Instead teleportation Narud receives 100% of the mana and health.(Trait)
Bolt of the Storm
Also I don't think Narud is the right guy for the job, he's much too cool to just be stealing other people's abilities. Maybe a Changeling would be better?
Do I need to give the button to cancel the skill? No no need. This is a complex character, and they need to play properly. And otherwise too much power for one hero. Moreover, the other characters can not even change the talents. A change in the ability to do would ruin any game, even with the terrible choice of heroes.