Centuries have passed since the old Demon King had been defeated. After a long struggle for influence (playable in Monster Hex), one of the 4 Demon Lords rises to become the new King.
In Dungeon Mahjong players are young adventurers delving into the Royal Dungeon to defeat the Monsters lurking within. Starting with a hand of 6 Guild Cards representing a party of followers from one of 5 classes (Thief, Warrior, Sorcerer, Knight and Monk, corresponding to numbers 1 to 5), each player on their turn chooses one of two actions:
Discard a Guild Card for its effects
Reveal a number of cards from the hand to defeat a Monster
The Monster Cards come in 3 levels, each requiring a matching number of Mahjong-like melds (either 3 sequential numbers, or 3 identical numbers), along with additional requirements, to defeat. Defeated monsters join the player's party to bring victory points and helpful special effects. Among the level 3 Monsters, there are the 4 Demon Lords, and to trigger the game end players need to defeat at least one of them (or at least 3 of the other level 3 Monsters). The player with the most victory points at the end of the game wins and is pronounced Hero.