To cast a spell, construct a triangle, also known as an asterism:
On the left hand corner, place a focus chosen from these Major Arcana (numbered zero to IX in many decks): The Fool, The Magician, The High Priestess, The Empress, The Emperor, The Hierophant, The Lovers, The Chariot, Justice, The Hermit.
On the right hand corner, place a fulcrum chosen from these Major Arcana (numbered X to XXI in many decks): Wheel of Fortune, Strength, The Hanged Man, Death, Temperance, The Devil, The Tower, The Star, The Moon, The Sun, The World.
At the top corner, place a cathexis chosen from any of the Minor Arcana (swords, wands, cups, or pentacles in most decks).
This spread determines what spell you cast. You might not know what it is till you try it. DMs may download the spell list here.
Tarot Cards as Artifacts
The simplest way to incorporate these cards into your campaign is to make them magic items.
Even a child can use enchanted tarot cards to cast a spell. All the spellcaster must do is grip the asterism in one hand, and incant the name of the cards in order. The figures on each card will come alive, just in time to perish. The cards will crumble to ash and the spell will spring into existence.
As the spell is released, the user of the tarot cards may pick the target. The effect occurs immediately, even when the spell would normally require a lengthy ritual.
A minor arcana card can often be bought or sold for its face value times ten in gold. A major arcana card usually costs between 100 to 500 gold. But like everything else connected to magic, these prices are fickle and unpredictable.
Sometimes, when a combination is triggered, the figure on the card will invert itself as it bursts into flames. For instance, whenever a healing spell is cast, if there is a Death card or a Hanging Man card involved, that card will invert itself.
It may be assumed that every combination has some deep logic to it, but only some of these are comprehensible to mortal minds. In the past, attempts to write up a grand unified system of tarot spellcasting have proven futile.
Tarot Cards as a Whole New Magic System
Alternatively, you could radically change the way magic works in your campaign. By this option, instead of the tarot cards being in-game equipment that the players' note down on their character sheets, the players use actual tarot cards as props to represent their characters' spellcasting abilities.
If you use this method, the spellcasters must pick the target before they find out for certain what the asterism represents.
1. The spellcaster starts off fragmentary knowledge of the occult (see The Wizard's Grimoire, The Paladin's Prayerbook, and the Bard's Spellsheets for examples. Also see the list of common associations). During their apprenticeship, they've never been able to tell when they are using magic, and when the magic is using them.
2. At the start of the campaign, each spellcaster gets dealt a hand of tarot cards. The amount of cards they get depends on their class and level. At level one, Clerics, Druids, Sorcerers, Warlocks, and Wizards get nine cards each, and Bards, Paladins, and Rangers get seven cards each. These maximum hand sizes go up by one at levels four, eight, and fourteen. Any remaining cards are placed in a face-down pile in the center.
3. See “Magic as Discovery" below for guidelines about spellcasting. Cards that get burned in spells go in a separate discard pile. Whenever the central pile runs out, or whenever the PCs have a long rest, shuffle the discard pile back into the main pile.
4. The PCs top up their eldritch energy when they spend hit dice during a short rest. Whenever any spellcaster spends any number of hit dice, that player may draw cards from the top of the central pile, restoring their hand to its maximum size. Before they do this, they may also discard any unwanted cards from their hand.
5. They can also do this whenever the PCs have a long a rest.
6. It's up to you whether you want to let players keep their hands from one adventure to the next.
7. If your group is chocka with magic folks, you may want to use two sets of tarot cards.
One major arcana is innate to each spellcasting class. This represents the core expertise of their art.
Bard: The Lovers
Cleric: The High Priestess
Druid: The Hermit
Ranger: The Chariot
Sorcerer: The Fool
Warlock: The Emperor
Wizard: The Magician
Some classes may gain more innate arcana at levels five, thirteen, and/or seventeen (see the full rules for more details).
A spellcaster may treat any card in their asterism as if it were their innate arcana.
For instance: Maggie is a druid. She constructs an asterism using the Three of Cups for her focus, Strength for her fulcrum, and the Five of Wands for her cathexis. Normally this wouldn't do anything -- you need a major arcana in the focus slot -- but Maggie uses her innate arcana to treat the Three of Cups as The Hermit. She casts Thorn Whip.
1. The spellcaster announces the target of the spell.
2. The spellcaster lays out the three cards of the asterism, as described above.
3. Magical energies gather inside the spellcaster. The DM tells them the name of the spell.
4. The spellcaster may be really happy about this, and complete the spell. (They may need to give the working a few finishing touches. For instance, if they are casting Teleport, although they have already chosen the target, now they may select their destination).
5. Or the spellcaster may regret their choice of target, and try to change it before the spell is cast. They must make a check on their spellcasting attribute (Intelligence, Wisdom, or Charisma). The DC is 10 + the face value of the cathexis card (court cards count as 11, so the DC is 21). This spiritual struggle happens instantaneously and doesn't require an action or bonus action. If they succeed, the spell can be diverted to the new target.
6. Or the spellcaster may have big regrets. Instead of trying to switch targets, they can try to cancel the spell completely. They do this by making a check on their spellcasting attribute (Intelligence, Wisdom, or Charisma). The DC is 10 + the face value of the cathexis card (court cards count as 11, so the DC is 21). This spiritual struggle happens instantaneously and doesn't require an action or bonus action.
- If this check succeeds, they burn their cathexis card (the minor arcana), but keep the other two cards (the major arcana). The spell is safely choked back.
- If the check fails, then the spell casts itself against their will. However, if they have a bonus action to spare, then they have one last chance to channel this eldritch retch away from its current target. This now requires a Dexterity check with a DC of 10 + the face value of the cathexis card.
Magic as Discovery
Under these laws, magic is perilous, wild, and unpredictable. Every spellcaster's capacity to wield magic is in constant flux. Doesn't that sound simply magical?
As a DM, keep the spell list secret from the players. Have them guess what different combinations do. Let them learn the hard way.
Even the most experienced spellcasters are sometimes at the mercy of the magic. Low-level spellcasters in particular may find themselves blurting devastating major workings with tragic consequences.
For more guidelines on things like casting time, range, level progression, collaborative spellcasting, and variants and optional rules, see the full rules.