Confidence:StrongSolidPlausibleTentativeSpeculative

• Ioreth of the Healing House✓

  2U

  Legendary Creature — Human ClericU

  Untap loop: each side can untap what the other taps — a genuine mutual refresh engine.
• Kiki-Jiki, Mirror Breaker✓

  2RRR

  Legendary Creature — Goblin ShamanR

  Copy chain: one card creates hasty copies of a creature whose ability or ETB the partner exploits — the canonical Kiki-Jiki / Splinter Twin pattern.
• Elvish Scout

  G

  Creature — Elf ScoutG

  Untap loop: each side can untap what the other taps — a genuine mutual refresh engine.
• Samut, Voice of Dissent

  3RG

  Legendary Creature — Human WarriorGRW

  Untap loop: each side can untap what the other taps — a genuine mutual refresh engine.
• Forensic Researcher

  2U

  Creature — Merfolk DetectiveU

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

  1G

  Creature — ElfG

  Untap loop: each side can untap what the other taps — a genuine mutual refresh engine.
• Nature's Chosen

  G

  Enchantment — AuraG

  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.
• The Moment

  2

  Legendary ArtifactC

  Untap loop: each side can untap what the other taps — a genuine mutual refresh engine.
• Saryth, the Viper's Fang

  2GG

  Legendary Creature — Human WarlockG

  Untap loop: each side can untap what the other taps — a genuine mutual refresh engine.
• Second Wind

  2U

  Enchantment — AuraU

  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.
• Norritt

  3B

  Creature — ImpB

  Untap loop: each side can untap what the other taps — a genuine mutual refresh engine.
• Stonybrook Angler

  1U

  Creature — Merfolk WizardU

  Untap loop: each side can untap what the other taps — a genuine mutual refresh engine.
• Vizier of Tumbling Sands

  2U

  Creature — Human ClericU

  Untap loop: each side can untap what the other taps — a genuine mutual refresh engine.
• Tideforce Elemental

  2U

  Creature — ElementalU

  Untap loop: each side can untap what the other taps — a genuine mutual refresh engine.
• Cursed Mirror

  2R

  ArtifactR

  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.
• Ith, High Arcanist

  5WU

  Legendary Creature — Human WizardUW

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

  LandC

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

  2U

  Creature — SpiritU

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

  2U

  Creature — Human WizardU

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

  2U

  Creature — Human WizardU

  Untap loop: each side can untap what the other taps — a genuine mutual refresh engine.
• Machine God's Effigy

  4

  ArtifactU

  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.
• Nanoform Sentinel

  2U

  Artifact Creature — RobotU

  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.
• Fatestitcher

  3U

  Creature — Zombie WizardU

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

  3

  ArtifactC

  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.
• Saheeli, the Sun's Brilliance

  UR

  Legendary Creature — Human ArtificerRU

  Copy chain: one card creates hasty copies of a creature whose ability or ETB the partner exploits — the canonical Kiki-Jiki / Splinter Twin pattern.

• WithTempestra, Dame of Games1RR

  Copy chain: each card copies the other (or both copy a third), generating arbitrary copies. These two can't keep the loop going alone — add one of these to complete it:

  Rose Room Treasurer3RSharp-Eyed Rookie1GKingpin, Wilson Fisk3BNuka-Cola Vending Machine3Gemcutter Buccaneer3RGala Greeters1G
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