Card of Darkness is a card-based dungeon crawling game. Each level is a 5x5 grid of card piles with each pile having 2 to 5 cards. Only the top cards are shown and only for the bottom row at first and later for any piles connecting to a blank space that you've cleared of cards. You have 20 hit points and no items and you're objective is to get to the exit stairs on the other side of the grid to get to the next level and eventually to the exit. A dungeon has 1 to 6 levels and there are 50+ dungeons.

Card types are weapons, monsters, heal potions and spell scrolls. Monsters have a damage rating and a weapon subtracts its rating from the monster rating. Using an even/odd weapon versus a non-matching even/odd monster breaks the weapon (e.g. weapon 5 versus monster 4 you take no damage but break your weapon). Spell scrolls are one use, have a set effect and in later dungeons are unknown (though confined to 2 or 3 effects) until you use one and then you now the exact spell for that scroll type.

Monsters are very varied. Some of the special abilities: poisons you, curses you (if you pick the same number card twice in a row you take damage equal to the number), confuses you (hides card types but not numbers for two or three turns), combines with nearby cards, randomly trades places with a nearby card, changes value based on other cards. The various monsters kind of develop personalities as you get to know their effects.

When you complete a dungeon you get a card of darkness and eventually there are 52. Before you go into a dungeon you can select which cards you equip (up to five). In the end I had

• Card of Life: max health +3 (to start with 23 hit points)
• Card of Strength: strength potions are +2 each (normal barehanded damage is 0, in some dungeons with enough strength potions you don't need weapons and your fists don't break)
• Card of Return: first time you are killed you revive with 1 hp (turns out rarely useful since if it gets to the point you die the freebie still leaves you with a level that will kill you immediately)
• Card of Stalwarts: cannot die from poison (this is a late game card and never used the effects but many monsters and some potions poison you)
• Card of Keeping: picking a new weapon does not replace your current weapon but instead adds 1 to current weapon value (another late game card and turned out extremely useful because you can pick up weapons to change your current weapon even/odd so it won't break)

Levels have a semi-random set of card types and randomly distributed so bad luck can get you killed quickly but you just restart and try again. Most dungeons you can finish within 5 minutes (and the game auto-saves your progress) and even the one tough 6-level dungeon probably took me 3 to 4 hours over a day or two to finally get a good combination of cards and a bit of luck.

Overall a fun game with just enough strategy to keep it interesting.