In the scene where Drogan (TJ Kayama) is talking to Mother Abigail (Whoopi Goldberg), he is kneeling as he recalls being with Flagg (Alexander Skarsgård). In the background when Flagg's hand touches his face you can see the carpet, which has the same print as the carpet in the Overlook Hotel in The Shining (1980).
Because "Ouija," is copyrighted by Hasbro, the game in this episode is the generically-named fictional version, "Planchette," and uses a prop previously seen in the third episode of PEN15 (2019).
Nadine (Amber Heard) uses a "Taduz planchette" to communicate with Flagg (Alexander Skarsgård). Taduz is the first name of the old gypsy who puts the wasting curse on Billy Halleck in Stephen King's novel "Thinner".