This quick solitaire game with a standard playing card deck doesn't have a BGG entry. In fact, I accidentally found it on YouTube, on a channel called Riffle Shuffle and Roll. It is dead easy to play, all you need is a pack of cards and ten minutes of your time.
Your enemies in the dungeon are represented by the court cards. You shuffle all the Kings, Queens and Jacks together, and lay 4 of them face down. Then the next four go on top of them face down, and the last four on top face up. You shuffle the rest of the deck which represents your attacks, and draw a hand of 3 cards. You're ready to go.
Jacks have 11 health, Queens 12, and Kings 13. If you have two cards the sum of which is equal to or above the health of a face up enemy, you place the cards on that enemy to attack them. Jokers are wild, and can become any value or suit from 1-10. The enemy is not killed, however, unless you give them the final blow: a card of a suit that matches the enemy's suit.
So, if, for example, you want to kill a Jack of Spades, you need to place two cards that add up to 11 or more on him, plus a spade card of any value. The enemy is then defeated, and you get to reveal the next one in line.
If your 3 cards don't allow a full attack, you may split the cards to deal partial attacks. So you can place, e.g. a 10 on a Queen, expecting that you will get at least a 2 in subsequent turns. Any cards you can't use are discarded. You continue in this manner until either you kill all the court figures and clear the dungeon, or your deck runs out and you lose. Wins and losses often come down to the very last cards.
This falls, for me, into the 'nice little game' category. Quick, easy, nothing special but not bad either. Give it a spin if you have a pack of cards at the ready.
Here is the gameplay video by The Lone Cardman: