There are a lot of design pitfalls though:
-The cards can generate numbers very much like dice, BUT you don't just want the tarot-ness to be a cosmetic gimmick. Wands and swords should matter and The Devil should not just mean "15".
-Onnn the other hand if the cards are always throwing their symbolic weight around then you risk having a resolution system where someone's trying to do a simple RPG crime-horror task like try to recognize a mugshot and the cards are suddenly like HAHA! THE EMPRESS! and then you have to deal with multiple layers of interpretation just to get through natural gameplay scenarios.
-The whole thing of the tarot is that it tells you what's going to happen, but...in RPGs (at least the kind I make) you aren't ever going to be able to completely predict what'll happen.
-You don't want to create a situation where the system is suddenly less flexible and less convenient than dice but basically doing the same things. Like I don't want anyone cheated out of a fun game just because I want some precious themes stuck in there.
-You don't want to make it a deck-building game. Distracting players from clever things their players are doing in the game with card-management tasks would be bad. Especially because this is not a game where most players throw magic around (except the occasional lone psychic or vampire character).
-I already have a gajillion d100 tables in Demon City, I'm not gonna knock them all back to d78 tables just for aesthetic consistency, that's some serious form-over-function.
-So: the cards need to be as intuitive and frictionless as dice, while still taking advantage of the special qualities and associations that tarot cards have.
And....I cracked it. There are no dice in Demon City now.
(Ok, actually I am building in a "dice option" that covers the same bases in case you're like at a con or game store and suddenly decide to play but there are no cards. But the default uses cards.)
Here's how cards work, basically. These aren't how the official rules in the book work but its a quick rundown of what you'll see in the current draft:
Part of the Hosts job is to take the full tarot deck and make mini-decks out of it to play with.
The first and simplest is the Character Deck, which just randomizes number for character gen. This solved a problem I was having before: I want numbers from 0 to 5 but I wanted extremes to be rare and I wanted the math to be simple. The character deck has 4 Aces, 4 twos, 4 threes, 3 fours and 1 five (of any suit) and The Fool (0). So then you just shuffle and pick your 7 attributes from the deck. Easy peasy. Hack-happy Hosts can even adjust the odds as they like manually to make more-instabadass or more-bathetic characters. This part actually makes dice-for-character-gen seem kinda like a kludge in comparison.
Real gameplay sees the deck used in more interesting ways:
The Host the makes a "Players' Deck" and a "Horror's Deck".
At the beginning, the Players' Deck just has 3 of each number (3 aces, 3 twos etc up to 10).
The Horror's Deck has one of each number Ace-10 plus any cards associated with the scenario and the specific Horror for that day, also the specific Ace through ten chosen will be the most thematically appropriate ones for the scenario. Advice on how to do that is laid out.
The Player's Deck sits in the middle of the table face down. Instead of taking set numbers of dice and--when its time to roll the Clash--everyone rolls dice and takes the highest, you take set numbers of cards off the top unseen and, when its time to resolve the Clash, flip them over and take the highest. The math is the same other than certain numbers slowly get depleted until you run out of cards and reshuffle.
The Horror's Deck is just used by the Host the same way. The Host, at least in the beginning, will have a few unbeatable cards (over 10) because hey it's a horror game. But they will pop up randomly rather than when the Host wants them to.
When a Big Bad is taken down, the Host fans out the Horror's Deck face down and each player gets to take one card.
This card is that PC's Significator (old tarot lingo). It gets put into the Players' Deck for next time. When you pop your own significator it's a crit for you, but each one also has a specific reward related to the card's occult meaning that can be called in at any time, which "burns" the significator and takes it out of the deck. You have to trade in your old Sig for a new one when you defeat the next menace anyway. While there's now several in the deck, each player only has one that applies to them at a time, so it doesn't become a whole thing of keeping track of cards.
The Fool also gets mixed in to the decks to act as a fumble (and yes, there's a rule for if the Fool is your Significator).
d100 rolls can be made from just taking 2 cards from the Players' deck (the Horrors' deck makes it harder to get repeated numbers like 44), one for each digit, 10=0 as usual.
And some monsters have a special mechanic for when one of the cards associated with them pops up.
Aaand other occult mechanics can be bolted on around predicting cards, seeing cards, which suits pop up, etc.
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