Confidence:StrongSolidPlausibleTentativeSpeculative

• Worzel, the Protector

  1WWW

  Legendary Planeswalker — WorzelW

  Untap loop: each side can untap what the other taps — a genuine mutual refresh engine.
• Harold and Bob, First Numens

  2G

  Legendary Creature — Treefolk MutantG

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

  6

  Artifact Creature — ConstructC

  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.
• 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.
• Elrond, Moon-Reader

  2U

  Legendary Creature — Elf NobleU

  Trade Caravan has activated abilities that aren't mana abilities, fueling Elrond, Moon-Reader's activation-trigger.
• Rings of Brighthearth

  3

  ArtifactC

  Trade Caravan has activated abilities that aren't mana abilities, fueling Rings of Brighthearth's activation-trigger.
• Illusionist's Bracers

  2

  Artifact — EquipmentC

  Trade Caravan has activated abilities that aren't mana abilities, fueling Illusionist's Bracers's activation-trigger.