The card deck comes with rules for a game called Prophet's Gambit, which is basically Texas Hold'em with a D&D twist. If you are into minigames have them play the game for high stakes.
You can also give the players the option to change their fate by getting a new reading.
I like your idea of having the high cards having special in-game effects, both good and bad.
Shuffle the cards well. If they draw from the lower deck nothing happens. But maybe you want every card to mean something. I would state the party somehow comes across a powerful deck of cards. They can use it once per in-game day. After drawing a card it disappears from the deck.
Lower Deck Effects (all effects last for 24 hours, any boons not used go away after 24 hours)
Swords
Master of Swords - player gets advantage on all Strength and Constitution skill checks and saving throws but disadvantage on skill checks and saves for all other attributes.
If one to five of swords is drawn (those with positive attributes according to their descriptions in the book), the person who draws gets a corresponding +1 to +5 on any one attack roll for that day.
Six of swords - gives the character who select the card the Barbarian "Rage" ability one time.
Seven of swords - suffers from paranoia and fear of unknown persons. For one day, any time the player encounters a new person, they must make a DC 15 saving throw or suffer the fear condition around that person. THey can make a new save check each turn. If they make the save, they are immune from the fear condition for that person only, but will have to make a new check for the next new person.
Eight of swords-- character gets an avantage on one intimidation check
Nine of swords-- the players suffers the effects of torture. 3d6 psychic damage and 2 levels of exhaustion.
Stars
Master of Stars - player gets advantage on all Intelligence skill checks and saving throws but disadvantage on skill checks and saves for all other attributes.
One to Five of Stars: +1 to +5 on any magic attack, save against magic, or arcana skill check--one time only and must be used in 24 hours since drawing the card.
Six of stars - roll on the Sorcerers Wild Surge table and apply the effect to the player who drew the card.
Seven of stars - character is unable to tell the truth for 24 hours
Eight of stars - character is unable to make any attacks or otherwise harm undead creatures - all undead immune from any damage caused by the character
Nine of stars - a shadow demon is summoned, surprises, and immediately attacks the character who drew the card
Coins
Master of Coins - player gets advantage on all charisma and dexterity skill checks and saving throws but disadvantage on skill checks and saves for all other attributes.
One to Five of coins. The player get 1 to 5 gold pieces.
Six of coins. All of the players coins disappear and are transported to the sealed treasury room of the Amber Temple (X40).
Seven of coins. The player suffers from kleptomania and must make a DC10 saving throw whenever he first sees anything made of precious metals or gemstones.
Eight of coins. The player is compelled to intimidate weaker people to give him money for "protection" or asks for more money than is reasonable for services or help. Will demand that any debts owed to him or her be immediately repaid.
Nine of coins. The player will refuse to spend money or give up anything of value, demanding other party members pay for anything.
Glyphs
Master of Glyphs - player gets advantage on all wisdom skill checks and saving throws but disadvantage on skill checks and saves for all other attributes.
One to Five of Glyphs. Player gets +1 to +5 on one Wisdom skill check or saving throw.
Six of Glyphs. On the next Wisdom saving throw or skill check made by the character, he or she must roll UNDER the DC value rather than over to succceed.
Seven of Glyphs. The character acts CONTRARY to their IDEAL (personality charcteristic) for 24 hours.
Eight of Glyphs. Character must act in a Lawful Good manner for 24 hours. Any time they attempt to steal, lie, initiate violence (as opposed to responding to or defending themselves or others), or otherwise act contrary to stereotypical lawful-stupid manner (as determined by DM fiat) they suffer 1d4 psychic damage and suffer disadvantage on any attack, skill check, or saving throw related to that non-LG behavior.
Nine of Glyphs. The character will be placed under a Geas, cast at 9th level to kill another party member, but this Geas only lasts for 24 hours. It can be ended by remove curse, greator restoration, or wish.
Higher Deck
The Artifact
One weapon of choice becomes a +3 weapon that does an additional 1d6 necrotic damage as it becomes infused with a chaotic evil spirit. It is impossible to knock out a creature when attacking with this weapon. You can only attack for damage. If anyone else touches or attempts to use the weapon, the attuned character must make a DC15 saving throw or go into a rage and attack whomever touched it. The player must make a DC20 Wis saving throw to allow the weapon to be more than 5' away. Once per day, the weapon will attempt to convince another party member or NPC to attempt to steal it away from the attuned player. Anyone subject to this subtle effect must make a DC 5 Wisdom saving throw. Rolling a 1 is an automatic failure.
The Beast
The player is stricken with Lycanthropy. Roll a 1d6 to determine what form:
- Werewolf
- Wereboar
- Werebear
- Wererat
- Weretiger
- Wereraven
See the Player Characters as Lycanthropes section in the Monster Manual for effects.
For wereraven: The character games a Dexterity of 15 if his or her score isn't already higher. Attack and damage rolls for the beak are based on whichever is higher of the character's Strength and Dexterity. Fly speed of 50' in raven or hybrid form. See the Wereraven entry in the Curse of Strahd book for other details.
The Broken One
The player succombs to the hopelessness that pervades Barovia. The player suffers the effects of indefinate madness as a coping mechanism. Roll on the indefinate madness table in the DMG.
The Darklord
Summons Strahd. Strahd gets no save and appears within 50' of the person who drew the card. How Strahd reacts to this is up to the DM.
The Donjon
The person who drew the card and anyone within 20 feet of him or her are teleported to K74e and the other empty cells in the North Dungeon of Castle Ravenloft. If the card is drawn in a location (like a crowded bar) with many people, spread them out among the empty cells.
The Ghost
The person who drew the card becomes a Ghost. They retain all their skills and knowlege, but can only use most of them when in possession of a body, using the possessed persons attributes. In ghost form they cannot cast magic and their only attacks are those provided by the Ghost entry in the monster manual.
The Executioner
A ghastly figure in a dark executioners mask and robe points at the player and, saying "
Judicaris, Poena mortis," and casts Power Word Kill before fading away.
Horseman
A paladin who broke his vows and stayed loyal to Strahd dies without ever seeking atonement and was brought back by the dark powers as a death knight. This is a Death Knight with the following changes:
1. It rides a Skeletal Warhorse. The warhorse is same as Warhorse Skeleton, except the AC is 18. Otherwise the horse is the same as in the MM. If the horse is destroyed, it reforms in two rounds unless 11 HP of damage is done in the round before reforming. The Death Knight can mount the horse as a bonus action.
2. It attacks with a lance. It only has a lance. It has no long sword and get's no multiattack. If it is fighting on the ground it has disadvantage on attacks against anyone within 5'. It can use its parry reaction as normal with its lance.
3. The Death Knight cannot willingly leave its mount. If the mount is destroyed, it will not chase fleeing party members until the skeleton reforms and it can remount it. If the party is attacking it, however it will close melee distance or use other tactics to defend regardless of the horse skeletons location. If the party takes the bones, it will always know where the bones are and track them down. If the party throws the bones of a ledge, cliff, in water, etc. and if the party then flees the Death Knight break of its attack to retrieve the bones.
4. The Death Knight if mounted, will not dismount to follow the party anywhere the horse is unable to go.
5. It is up to the DM whether the Death Knight will attempt to track the party until it is dead and become a recurring threat.
The Skeleton Warhouse is meant to give the party a chance to escape from what is an over-powered encounter for this adventure.
The Innocent
Choose one good/helpful NPC. For example, Irena if the party failed to protect her. Or Gertruda. Or to help the party find Esmeralda or Van Richten. The person who drew the card experiences the effects of the "Find the Path" spell, except that instead of a fixed location, it shows the most direct and quickest route to the location of that person, wherever that person is, even if that person changes locations. The duration is the lifetime of the target-person OR it ends when the person is encountered, whichever comes first.
The Marionette
A Flesh Golem appears. The character that drew the card becomes the creator/possessor. If the party makes no attempt to disguise its nature, the NPC will mob the players and golem to destroy it. If disquised, there is a 5% when in a populated area of someone recognizing the person whose corpse it is.
The Mists
The player falls under a geas to travel to a level-appropriate location in Barovia and complete a major quest from that section.
The Raven
A were raven appears that is under geas to help the party, it will feel that it was called by a higher power of good to give all its efforts to assist the party.
The Seer
The location of any unfound item from the fortunes of ravenloft is revealed to the party. Otherwise the location of any other powerful item or helpful person is revealed.
The Temptress
A succubus/incubus will appear as an attractive humaniod of the same race as the character who drew the card. It will pretend that the character summoned it to barovia and seek the parties protection and offer to help until it can get the character alone to attempt to charm and use its draining kiss attack. It will act as if it is charmed by the player. Try to get the player t o believe that he or she summoned this person and has them under a permanent charm effect. If found out, it will plead for its life. It will offer to help the party stating that it was indeed summoned by the card and is now stuck in Barovia. It needs the party to defeat Strahd to escape barovia. This is not a lie. If strahd become aware if its presence in Barovia, he will want to possess and control it. The succubus will continue to help the party so long as it is in its insterest to do so. If brought into contact with the Vistani, it will attempt to charm them to get one of them to take it out of Barovia.
