Engineer by Masterjojojo

Engineer can use his heroic ability to get 1 charge. Once engineer activates this, all lanes will explode dealing 4000 (+100 p/ lvl.) damage to all minions, mercs and structures.

This seems OP, but reading the heroic ability will make you change your mind.
Forts have 10k health and keeps 14.5k

Stick explosives on an enemy. After 3 seconds or when you reactivate the ability, these explode dealing 60 (+8 p/ lvl.) damage.

Mana: 60
Cooldown: 5 seconds

Increase the damage dealt by nearby units by 25% and reduce the damage taken by 25% for 5 seconds.

Mana: 50
Cooldown: 10 seconds

Repair an allied structure for 100 (+10 p/ lvl.) health and 1 ammo per second. Cannot heal the structure if it's above 50% health.

Mana: 10 p/ second
Cooldown: 15 seconds

Channel for 60 seconds to get 1 charge of The Master Plan. You can't use this inside your base and during this time the enemies have vision in a medium area around you. The only way to stop the channel is by killing you.

During the channel you should have the help of your allies to protect you from death.
Lvl. 20 talent allows you to save 50% of the progress of the channel.

Mana: 100
Cooldown: 100 seconds

Kill 100 (15 waves) minions with Sticky Explosives to get 1 charge of The Master Plan. You lose all stacks after death.

Lvl. 20 talents allows you to save 50% of your stacks.

Mana: [Passive]
Cooldown: [Passive]