Confidence:StrongSolidPlausibleTentativeSpeculative

• Innkeeper's Talent

  1G

  Enchantment — ClassG

  Counter synergy: both cards work with the same kind of counters, so their effects stack in a counters deck. Not necessarily a closed loop on its own.
• Hela, Mistress of Darkness // Dark Tutor

  4BB1BB

  Legendary Creature — God Sorcerer Villain // Sorcery — VengeanceB

  Both cards trigger on life loss — they fire together.
• Sahir, Visitor in Darkness

  1BB

  Legendary Creature — Human WizardB

  Both cards trigger on life loss — they fire together.
• The Master of Lake-town

  1BB

  Legendary Creature — Human AdvisorB

  Both cards trigger on life loss — they fire together.
• Ob Nixilis, Captive Kingpin

  2BR

  Legendary Creature — DemonBR

  Both cards trigger on life loss — they fire together.
• Marina Vendrell's Grimoire

  5U

  Legendary Artifact — BookU

  Both cards trigger on life loss — they fire together.
• Mirror Room // Fractured Realm

  2U5UU

  Enchantment — Room // Enchantment — RoomU

  Mirror Room makes Font of Agonies's triggered ability trigger an additional time — each time it fires, you get it twice. Value, not a loop.
• Lich's Mastery

  3BBB

  Legendary EnchantmentB

  Both cards trigger on life loss — they fire together.
• Vilis, Broker of Blood

  5BBB

  Legendary Creature — DemonB

  Both cards trigger on life loss — they fire together.
• Gonti's Machinations

  B

  EnchantmentB

  Both cards trigger on life loss — they fire together.
• Moonstone Harbinger

  2B

  Creature — Bat WarriorB

  Both cards trigger on life loss — they fire together.
• Vengeful Warchief

  4B

  Creature — Orc WarriorB

  Both cards trigger on life loss — they fire together.
• Vampire Scrivener

  4B

  Creature — Vampire WarlockB

  Both cards trigger on life loss — they fire together.
• Transcendence

  3WWW

  EnchantmentW

  Both cards trigger on life loss — they fire together.
• Rings of Brighthearth

  3

  ArtifactC

  Font of Agonies has activated abilities that aren't mana abilities, fueling Rings of Brighthearth's activation-trigger.