Scoundrel

Single player dungeon-crawling card game using the standard "Joker" deck. Go through a dungeon, pick up weapons, fight monsters, drink potions, try to survive!

The game has simple rules. It is also easily extensible with custom rules to tune the difficulty and/or complexity to your liking.

Core rules

Extension rules

Trying out different rule "modules" is a fun way to enjoy the game even more.

Discarding weapons

Why equip a dagger when you're holding an epic broadsword?

New option: discard a weapon card instead of equiping it.

Blacksmiths

The diamond face cards are blacksmiths who can repair or improve your weapon.

diamond face cards are kept in the deck
blacksmith gets rid of monster card off of an equipped weapon: Jack 1, Queen 2, King 3, and Ace all.
if a weapon has no durability loss, you can place a blacksmith under it to give it a bonus based on the value of the blacksmith: J +1, Q +2, K +3, A +4.
blackmith can be chased away, discarding the card without using its effect.

Merchants

The heart face cards are merchants who trade your weapon for a healing potion.

heart face cards are kept in the deck
merchant discards your weapon and gives a health bonus equal to the weapon's rating, minus the number of monster cards on it, plus the merchant modifier (J +0, Q +1, K +2, A +3).
merchant can be chased away, discarding the card without using its effect

Companions

Jack joins your party as either a fighter or a healer.

Jack cards are kept in the deck
Jack becomes a companion and can be given a weapon or a potion.
- Companion with a weapon acts as a second player weapon. When used to fight a monster with higher damage, the companion dies (gets discarded) and the player takes the rest of the damage as usual.
- Companion with a potion provides a one time health boost and then gets discarded.

Links to sources

After looking at these comments I've started using a couple of the home rules they did (But I made some minor edits so they'd work together). 
- The diamond face cards as the blacksmiths (exactly how romanallgeier4661 did, so the Jack gets rid of one monster card off of an equipped weapon, Queen 2, King 3, and Ace all). Also, if a weapon has no durability loss, you can place a blacksmith under it to give it a bonus based on the value of the blacksmith, Jack is +1, Q +2, K+3, A+4. Being upgraded by an Ace also means that the weapon can attack an enemy that it one greater than its durability allows (this bonus is kinda situational but when it pays off it feels awesome and it means you can chain back up if you set it up right)
- The heart face cards as merchants as 4TheWizard said, with them allowing you to 'sell' weapons for health back, but with the amount of health back being the power of the weapon minus the amount of monster cards attached (with a lower cap of one health gained of course) plus a bonus based on the relative value of that face card (with jack having no bonus, queen adding 1 extra health, king adding 3 extra, and ace adding 5). 
- The party member idea of StartTheDayWithKeele could be used by the jokers, the red joker carrying potions that could be used later and the black joker carrying weapons so that you'd have more options in combat (tho he'd only be able to do combat that results in him not taking any damage or he dies and is discarded) or you could also (as if you have a d20 you probably have a full set of DnD dice) you could use a d8 (or some other value depending on what you think his health should be) and give him hp independently. 
Just wanted to put all of these ideas in one place as I thought they were really fun and meant I didn't have to search through all my cards each time looking for the red face cards lol. Also, for these rules, if you come across a diamond or hearts face card and are unable to or don't want to use them for any reason then you can recycle them into a random part of the deck (they don't have to go to the back because they can wander around the dungeon--this also means that if you run away from a room they won't go in the back, but will go somewhere random in the deck), but if you use one then it is gone forever.