Confidence:StrongSolidPlausibleTentativeSpeculative

• Umbral Mantle✓

  3

  Artifact — EquipmentC

  Untap loop: each side can untap what the other taps — a genuine mutual refresh engine.
• Staff of Domination✓

  3

  ArtifactC

  Untap loop: each side can untap what the other taps — a genuine mutual refresh engine.
• Sword of the Paruns✓

  4

  Artifact — EquipmentC

  Untap loop: each side can untap what the other taps — a genuine mutual refresh engine.
• Crab Umbra✓

  U

  Enchantment — AuraU

  Untap loop: each side can untap what the other taps — a genuine mutual refresh engine.
• Baron Helmut Zemo

  BBB

  Legendary Creature — Human Noble VillainB

  Copy engine: one card makes a copy of a creature every turn, and the other's enter-the-battlefield effect rewards each copy. Real, repeatable value — the partner can't untap or re-enter the copier, so it never goes infinite.
• Tinybones Joins Up

  B

  Legendary EnchantmentB

  Both cards trigger when a creature enters the battlefield — they fire together.
• Chandra, Flameshaper

  5RR

  Legendary Planeswalker — ChandraR

  Copy engine: one card makes a copy of a creature every turn, and the other's enter-the-battlefield effect rewards each copy. Real, repeatable value — the partner can't untap or re-enter the copier, so it never goes infinite.
• Spreading Plague

  4B

  EnchantmentB

  Both cards trigger when a creature enters the battlefield — they fire together.
• Season of Growth

  1G

  EnchantmentG

  Both cards trigger when a creature enters the battlefield — they fire together.
• Kiora, Behemoth Beckoner

  2G/U

  Legendary Planeswalker — KioraGU

  Both cards trigger when a creature enters the battlefield — they fire together.
• Kiora, Master of the Depths

  2GU

  Legendary Planeswalker — KioraGU

  Both cards trigger when a creature enters the battlefield — they fire together.
• Faramir, Steward of Gondor

  1WU

  Legendary Creature — Human NobleUW

  Both cards trigger when a creature enters the battlefield — they fire together.
• Warden of the Grove

  2G

  Creature — HydraG

  Both cards trigger when a creature enters the battlefield — they fire together.
• Copperhorn Scout

  G

  Creature — Elf ScoutG

  Copperhorn Scout untaps all (or many) permanents, refreshing Heronblade Elite's tap activation.
• Grist, Voracious Larva // Grist, the Plague Swarm

  G

  Legendary Creature — Insect // Legendary Planeswalker — GristBG

  Both cards trigger when a creature enters the battlefield — they fire together.
• Fecund Greenshell

  3GG

  Creature — Elemental TurtleG

  Both cards trigger when a creature enters the battlefield — they fire together.
• Elvish Scout

  G

  Creature — Elf ScoutG

  One-directional refresh: one card can untap permanents the other wants to reuse. Not self-sustaining on its own — the untapper has to keep showing up.
• Lonis, Cryptozoologist

  GU

  Legendary Creature — Snake Elf ScoutGU

  Both cards trigger when a creature enters the battlefield — they fire together.
• Gladewalker Ritualist

  2G

  Creature — ShapeshifterG

  Both cards trigger when a creature enters the battlefield — they fire together.
• White Plume Adventurer

  2W

  Creature — Orc ClericW

  White Plume Adventurer untaps all (or many) permanents, refreshing Heronblade Elite's tap activation.
• Garruk's Uprising

  2G

  EnchantmentG

  Both cards trigger when a creature enters the battlefield — they fire together.
• Sunstrike Legionnaire

  1W

  Creature — Human SoldierW

  Both cards trigger when a creature enters the battlefield — they fire together.
• April O'Neil, Live on the Scene

  1U

  Legendary Creature — Human DetectiveU

  Both cards trigger when a creature enters the battlefield — they fire together.
• Brainstealer Dragon

  5BB

  Creature — Dragon HorrorB

  Both cards trigger when a creature enters the battlefield — they fire together.
• Prowl, Stoic Strategist // Prowl, Pursuit Vehicle

  3W

  Legendary Artifact Creature — Robot // Legendary Artifact — VehicleW

  Both cards trigger when a creature enters the battlefield — they fire together.