To get this you need to play 1000 games through the Multiplayer button on the main menu. Note that you do not need to win or even to actually play against humans. You can simply set up a private empty lobby, start the game, and immediately resign over and over.
However you go about it, you should get this while going for the game mode achievements:
The Anytime, Anywhere achievement in Age of Empires II (2013) worth 59 pointsYou have fought on every type of map, against every type of opponent in history. There may be those who will still stand against you, but they do so with respect. Huzzah!
The Deathmatch Legend achievement in Age of Empires II (2013) worth 56 pointsAfter 300 battles if there is something to be learned in Deathmatch it is where to find opponents who will still agree to fight you. Congratulations!
The One Hundred Hills achievement in Age of Empires II (2013) worth 56 pointsYou have claimed one hundred hilltops! The victor isn’t often the first one to the top, but the one that knows how to hold it once they are there. You have demonstrated that knowledge. Cheers to you!
The Wonder Race Mastery achievement in Age of Empires II (2013) worth 53 pointsFor many, the Wonder Race is a good way to learn how to tune an economy and know the short path to the Wonder for any civilization. For you, the Wonder Race has its own appeal - a celebration of the empire builder’s art. Congratulations!
The Lightning General achievement in Age of Empires II (2013) worth 58 pointsYou are an expert at the Turbo style, your decision-making under time pressure is legendary. Congratulations to you, Lightning General!