Confidence:StrongSolidPlausibleTentativeSpeculative

• Mikaeus, the Unhallowed✓

  3BBB

  Legendary Creature — Zombie ClericB

  Death replacement: a death-replacement grant on one card lets the other repeatedly die-and-return for combo (Mikaeus + Walking Ballista class).
• Court of Garenbrig

  1GG

  EnchantmentG

  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.
• Hollowmurk Siege

  BG

  EnchantmentBG

  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.
• Sazh Katzroy

  3G

  Legendary Creature — Human PilotG

  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.
• Heliod, Sun-Crowned✓

  2W

  Legendary Enchantment Creature — GodW

  Counter + damage loop: one card spends counters to deal damage while the other replaces them on a hit (Heliod + Walking Ballista class).
• Benevolent Hydra✓

  XGG

  Creature — HydraG

  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.
• Bristly Bill, Spine Sower

  1G

  Legendary Creature — Plant DruidG

  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.
• Zimone, Paradox Sculptor

  2GU

  Legendary Creature — Human WizardGU

  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.
• The Destined White Mage✓

  2W

  Legendary Creature — Human ClericW

  Counter + damage loop: one card spends counters to deal damage while the other replaces them on a hit (Heliod + Walking Ballista class).
• Ornery Tumblewagg

  2G

  Creature — Brushwagg MountG

  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.
• Vigor✓

  3GGG

  Creature — Elemental IncarnationG

  Counter + damage loop: one card spends counters to deal damage while the other replaces them on a hit (Heliod + Walking Ballista class).
• Hydra's Growth

  2G

  Enchantment — AuraG

  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.
• Byrke, Long Ear of the Law

  4GW

  Legendary Creature — Rabbit SoldierGW

  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.
• Ruinous Waterbending

  1BB

  Sorcery — LessonB

  Both cards trigger when a creature dies — they fire together.
• 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.
• Turtle Van

  3

  Artifact — VehicleC

  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.
• Level Up

  1G

  Enchantment — AuraG

  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.
• The First Tyrannic War

  2GUR

  Enchantment — SagaGRU

  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.
• Sword of Hours

  2

  Artifact — EquipmentC

  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.
• Seismic Tutelage

  3G

  Enchantment — AuraG

  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.
• Arcade Cabinet

  3

  ArtifactC

  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.
• Haunted One

  2B

  Legendary Enchantment — BackgroundB

  Both cards trigger when a creature dies — they fire together.
• Heart-Shaped Herb

  4

  ArtifactC

  Counter + damage loop: one card spends counters to deal damage while the other replaces them on a hit (Heliod + Walking Ballista class).
• Bretagard Stronghold

  LandGW

  Counter + damage loop: one card spends counters to deal damage while the other replaces them on a hit (Heliod + Walking Ballista class).
• Chandra, Torch of Defiance

  2RR

  Legendary Planeswalker — ChandraR

  Chandra, Torch of Defiance produces damage that can kill creatures, enabling Deathbringer Thoctar's death-trigger or removal payoff.