OpenAi developed an AI that wins agains the best professional dota 2 players in the world in 1-on-1 games. It does not use imitation-learning or tree search to learn. Instead it learns by playing agains a copy of itself continuously improving. The game is very complicated and if you would code the ai by hand you would maybe create a quite poor player. By having the computer to teach itself to play it learns a lot of tactics.
read more at:
https://blog.openai.com/dota-2/
Here are tactics it learned by itself: