26 cards where the card is tagged “synergy-room”

Balemurk Leech (Duskmourn: House of Horror #84)
Central Elevator // Promising Stairs (Duskmourn: House of Horror #44)
Creeping Peeper (Duskmourn: House of Horror #46)
Cult Healer (Duskmourn: House of Horror #2)
Dashing Bloodsucker (Duskmourn: House of Horror #90)
Entity Tracker (Duskmourn: House of Horror #53)
Erratic Apparition (Duskmourn: House of Horror #54)
Fear of Infinity (Duskmourn: House of Horror #214)
Fear of Sleep Paralysis (Duskmourn: House of Horror Commander #12)
Ghostly Dancers (Duskmourn: House of Horror #13)
Ghostly Keybearer (Duskmourn: House of Horror #61)
Gremlin Tamer (Duskmourn: House of Horror #215)
Infernal Phantom (Duskmourn: House of Horror #141)
Inquisitive Glimmer (Duskmourn: House of Horror #217)
Intruding Soulrager (Duskmourn: House of Horror #218)
Keys to the House (Duskmourn: House of Horror #251)
Marina Vendrell (Duskmourn: House of Horror #221)
Mothlight Processionist (Alchemy: Duskmourn #3)
Optimistic Scavenger (Duskmourn: House of Horror #21)
Rampaging Soulrager (Duskmourn: House of Horror #151)
Scrabbling Skullcrab (Duskmourn: House of Horror #71)
Skullsnap Nuisance (Duskmourn: House of Horror #234)
Smoky Lounge // Misty Salon (Duskmourn: House of Horror #235)
Stalked Researcher (Duskmourn: House of Horror #73)
Unwilling Vessel (Duskmourn: House of Horror #81)
Victor, Valgavoth's Seneschal (Duskmourn: House of Horror #238)

Though this query has ended, its relics still slumber in New Argive.