Playing cards are broken down by suit. Unfortunately ways to track which specific cards you're missing in game are limited, but this guide should still be helpful for tracking down a few of the trickier ones. Some of the cards do unlock brochure entries, so those can be checked easily. Screenshots are included for the cards with no easy point of reference for the rooms they're found in.

Note: A full list of cards you have already collected can be found by opening your save file in notepad. Cards collected are listed with the prefix "item_card_" followed by suit (h, d, c, s) and value (2-10, J, Q, K, A)

Clubs
A - On top of CCTV 2. Turn the camera off to make it fall to the floor.
2 - In the theatre fireplace. Must be collected before the King of Clubs Staff Member lights the fire at 7:30PM
3 - On the floor in the hallway leading to the guest rooms area, behind the Casino Code door.
4 - On the floor in one of the glass walkways in the basement. Only accessible through mirrors.
5 - On the floor in the hallway behind the theatre stage.
6 - On the floor in the main library, in the room with the ghost and the chandelier.
7 - On the floor in the chapel waiting room. Only available on return to chapel.
8 - On the floor in the room where Trinity is at the start of the day.
9 - On the floor in the small room to the left of the Grand Lobby room with the clock.
10 - In this room, with the padlocked entrance to the main library, examine the bookshelf.

J - On the floor in the upper garden area, just past the large window.
Q - In the locked chest in this room, behind the south Casino Code door.

K - Talk to this ghost.


Hearts
A - In the card vortex room in the basement. Only accessible after collecting the 10, Jack, Queen and King of Hearts.
2 - On the floor in the room where Clay Rockridge is playing cards.
3 - On the floor in the room with the portrait of the Marquis, where you can spy on the dining room.
4 - On the floor, on the balcony above the Grand Lobby, accessible from the Guest Area.
5 - Shatter the mosaic urn in the Heaven and Hell Staircase mirror room.
6 - On the floor in this room in the basement.

7 - Examine the costume rack in this room.

8 - Shatter the mosaic urn in the Casino mirror room.

9 - In the fireplace in this room. Must be collected before the King of Clubs Staff Member lights the fire at 5:30PM. Room accessible from the balcony of the large room with the phoenix elevator, in the Heaven and Hell Staircase area.

10 - Collect the roulette ball from the basement room with the broken robot. Use the ball on the pinball machine in the basement.
J - On the floor in one of the upper basement mirror rooms. Only accessible through mirrors.
Q - Examine the open book in this room.

K - Shatter the mosaic urn, in this room in the theatre.


Diamonds
A - Inside the locked chest in this room in the basement

2 - In the hidden dumbwaiter compartment where the staff member hides the Knight Statue's arm. Can only be collected BEFORE the staff member hides the arm.
3 - On the floor, in the same room as the fireplace with the 9 of Hearts.
4 - On the floor in the Grand Lobby room with the huge window.
5 - On the floor in the room with the "Devil's Monarch" fish.
6 - On the floor in the small room with the bar, where Auram gets a drink from the Ace of Spades Staff Member.
7 - On the floor in the basement mirror room.
8 - On the floor in this room in the theatre

9 - On the floor in the Music Rooms supply closet, where the idle gramophone is.
10 - On the floor, after going up the stairs to the Guest Area.
J - Shatter the mosaic urn in this room.

Q - In the gramophone room in the basement, run on the turntable for a bit and the card should show up.
K - The chapel, near the end of the game. Light the candle in the room with the stained glass window and talk to the ghost playing the organ.

Spades
A - Shatter the mosaic urn in this room.

2 - Inside the locked chest in the theatre lobby, where the clock is.
3 - In this bookshelf in the basement, after escaping the theatre.

4 - On the floor in the basement room with portraits of all the guests.
5 - In this hallway (north of the library clock room), examine the table in the center.

6 - On the floor on the balcony above the Grand Lobby Entrance. Visible at the start of the game, after the tutorial. Accessible from the Guest Area.
7 - On the floor in the room to the north of the Casino Entrance.
8 - Examine the left bookshelf in this room.

9 - On the floor in this room, East of the Library mirror room.

10 - In the hallway directly below the Casino Camera room on the map, there is a fireplace. The card can be found in the fireplace. Note, this is time sensitive: The card cannot be collected after the King of Clubs Staff Member lights the fire at 3PM.
J - On the floor in the What's Your Poison bar.
Q - On the floor in the Band Room, West of the Music Rooms entrance
K - Inside the locked chest in the room with the "Devil's Monarch" fish.

There are nine invitations in the game, one for each guest of the hotel. Five guests have their invitations with them, and four do not. You can check which invitations you have already collected by looking in the brochure - guests with uncollected invitations will have their entries locked.

Reginald Sixpence, Clay Rockridge, Trinity Carrington, Redd Rockridge:
These guests are simplest. Once they have died, examine their body to find the invitation. Make sure you wait a while before trying to get Trinity's: she doesn't die immediately, and her mask will still chase you. Same goes for Redd.

Willow Blue:
Talk to Grinmaw after Willow leaves the room with his tank, then collect the invitation from the top of the tank. You will need to have saved Willow and collected her mask before you can get this invitation.

Tequila Belle:
Talk to the ghosts in the room where Tequila is killed. The one by the Piano will give you her invitation.

Greyson Grayson:
His invitation is kept in the chapel safe. You need to open the safe before Reginald Sixpence does, so this can only be done near the end of the game.

Aurum Runes:
While Aurum is walking through the ballroom on his return trip, if Willow's candle is lit, you can see one of the ghosts go up and pickpocket him. Talk to this ghost while holding the hungry charm and he will trade you the invitation for it. The charm does not need to be satiated.

Thanos Gorecki:
The invitation is on his body, but you can't just wait until he dies and then go collect it. Thanos' body comes out in the basement, so you'll need to have saved him and reached the basement before you can collect his invitation. Just wait for the elevator to fall down from above, then get the invitation.