Card fight game..
Think Magic the Gathering, Yugi-Oh, Hearth Stone, Digimon, or the likes of it.
I dont exactly know how to play the game but if i remember correctly, @aggroed basically said "lets do a MtG on the Steem blockchain and thus SteemMonsters was born.
It's like a trading card game, but a bit easier than most. You basically build a deck that fights against the opponent's deck, and one of you will beat all the other cards of the other player.
If you have ever played Hearthstone, Gwent, Magic the Gathering or anything like that, than you will be familiar with the genre.
The big difference is that building the deck is the main part of the game on Steem Monsters, and there's no actual gameplay after the match has started. It's instead completely automated, so it's a lot more chill to play than other trading card games, which involved a huge amount of strategy.