Playing Cards appear on several occasions during our journey through the Realms of the Haunting. This article shall elaborate on the various instances and circumstances in which they are presented to us, and further discuss their potential meaning in the context of the game.
Ace of Spades[]
The Ace of Spades is the playing card which Gaul drops by the main entrance in the Mansion's vestibule, as seen in 
Gaul - 'Coming Events...'. Upon investigating the Armoury, Rebecca takes Adam's hand in order to telegraph Gaul's presence outside the house and his sealing of the double-winged entrance with one of the 
red lemniscatic wards that can also be frequently seen in Charles Randall's Vicarage. On the front side of the playing card which he drops in the process is written: "Adam, now it begins," leading Adam to speculate that Gaul may be an old friend of his father or someone who visited when he was too young to remember.
In folklore, the Ace of Spades is also referred to as "death card". Together with the 
Die we find in a small locker in the house, we could read the playing card as another ominous insinuation, a threat, a warning of impending death, disguised in the form of a pun.
Queen of Hearts[]
The Queen of Hearts appears during the final gathering with Florentine, Gaul and Hawk in the Chamber of the Soulstone, as seen in Endgame - Sorceror cutscene. In the context of the game, it represents Rebecca, alluding to the faint romantic bond that has manifested itself between her and Adam during their journey. Answering Adam's concerned question as to what happened to her, Gaul mockingly drops the Queen of Hearts playing card into the abyss that surrounds the green dome, as an implication of her death.
Joker[]
The Joker appears during the culminating confrontation with Florentine, Gaul and Hawk, in the Chamber of the Soulstone, as seen in Endgame - Keeper of Eternity cutscene. We can read the card as a representation for Rebecca and Aelf who under certain circumstances (i.e. by choosing the right branch of the conversation tree), come to Adam's assistance and help him defeat Florentine, subsequently averting Gaul's initiation as the new host for the power of Satan.