A Dota 2 custom game mode designed by China-based Drodo Studio is taking the Dota 2 world by storm, reaching 100,000 concurrent players earlier today and racking up over 670,000 subscribed users. Dota Auto Chess is a strategic, tactically complex mix of board game and Dota custom map. Play is based around drafting hands of heroes, combining them to upgrade them, and then deploying them correctly to win victories over eight other players in a series of one-on-one matches. The game has become wildly popular, with more concurrent players today than, say, Grand Theft Auto 5 or Football Manager 2019. Like Dota 2, Dota Auto Chess is completely free.

Dota Auto Chess is a weird name for it, I’ll grant. That makes sense since it’s cross-cultural, but the game doesn’t really have that much to do with a match of chess other than an 8x8 board. In truth, it inherits more from tactical board games like Neuroshima Hex or Warcraft 3 mods like Legion TD and Hero Line Wars.

Each round of the game you’re drafted a random hand of heroes you can buy using gold you’ve accumulated. Those heroes are then deployed to the grid and fight automated battles against each other. If you buy three of a specific hero, like Axe the Orc Warrior, you can combine them into a more powerful version of that hero. If you own three of a hero type, you get a bonus to that hero type—three warriors nets you +8 armor, for example. Each hero also has a race, with three of a race getting a bonus—so three Orcs nets you +250 health for all Orcs.

Did I mention that the draft is timed? It’s timed. You have 30 seconds to buy and combine, and you need to watch what enemies are drafting because there are only 20 of each hero available in the whole game. If others pull and buy the pieces of your combo from the pool before you then you're out of luck.

See where this gets complex? You’re simultaneously trying to beat enemies as cheaply as possible to save gold for later rounds while you build up combos and counter-combo what your enemies are doing. Got enemies with lots of stuns? Well, maybe you should aim for some Nagas and get stun resistance.

It’s a fascinating game, and rounds play so quickly that you can’t help but keep playing more of the game’s mini-tournaments. You don’t have to be great at Dota 2 to win, because the game automatically fights for you using the heroes you’ve deployed. Lose once from a bad hand? Well, just jump into another match and go for it again. Fights against neutral creeps break up the fights with players and net you bonus gold, so the pressure isn’t always completely on.

Here’s a bit of an explainer from Team Secret Operations Director Matthew Bailey:

Dota Auto Chess is one of the fastest growing games in 2019 & the majority of the gaming industry have no idea it exists.A @DOTA2 custom game built by Drodo Studio (a group of Chinese developers) that broke 100k concurrent users earlier today and has over 672k subscribed users. pic.twitter.com/RTTRucRFVYJanuary 13, 2019

You can find Dota Auto Chess here on Steam, or in-game in Dota 2's workshop.