The final confrontation in Thunderstone Quest is with the Guardian.
The three Monster decks in the Dungeon have six Keys hidden within them. When the fourth key is revealed from a Monster deck the Guardian appears in the Wilderness. Once the Guardian has appeared each player has the opportunity to either attack the Guardian or have one last visit to the Dungeon and then the game ends.
In the final turn each player performs their normal card draw and draws an additional four cards and then discards down to their current hand size. This means that on the final turn each player has the opportunity to get a great starting hand to defeat the Guardian.
The Guardian is not removed when defeated by a player. If a player beats the Guardian that player will be amply rewarded. But the rewards for the Guardian scale, based on how successful the player is. Each player has an opportunity to earn those rewards independent of the others. Players are not compelled to fight the Guardian. After a player has assessed their final draw they can choose to take a final Dungeon turn instead of confronting the Guardian.
Each Quest comes with three versions of the Guardian, each of slightly different difficulty, meaning that different Adventures within the Quest have a scaling challenge.
Once each player has either fought the Guardian or taken a final turn in the Dungeon the game ends and Victory Points are totaled to determine the winner.
We think the appearance of the Guardian provides a dramatic conclusion to the game. Players are building their decks to attempt Side Quests and to achieve Guild Quests but the biggest rewards come from defeating the Guardian which provides an excellent comeback mechanic and increases the suspense about who will win when the Victory Points are finally tallied.
— Mark Wootton
Thunderstone Quest Project Lead