it's a browser-based pick-up-and-play minesweeper-like where you kill monsters in a dungeon, with the end goal being to beat the dragon in the middle of the board.
you advance by killing monsters hidden on the board, which do damage and give xp equal to their health. so you can only attack monsters at or below your current health. leveling up increases your health. open tiles show not how many monsters are hidden nearby, but their total health.
a good run takes around 7 minutes. getting a good run can take like 30.