Confidence:StrongSolidPlausibleTentativeSpeculative

• Voltaic Key

  1

  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.
• Intellectual Offering

  4U

  InstantU

  Intellectual Offering untaps all (or many) permanents, refreshing Giant's Boulder's tap activation.
• Unstoppable Plan

  2U

  EnchantmentU

  Unstoppable Plan untaps all (or many) permanents, refreshing Giant's Boulder's tap activation.
• Manifold Key

  1

  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.
• Captain of the Mists

  2U

  Creature — Human WizardU

  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.
• Sonic Screwdriver

  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.
• Galvanic Key

  2

  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.
• Seedborn Muse

  3GG

  Creature — SpiritG

  Seedborn Muse untaps all (or many) permanents, refreshing Giant's Boulder's tap activation.
• Unwinding Clock

  4

  ArtifactC

  Unwinding Clock untaps all (or many) permanents, refreshing Giant's Boulder's tap activation.
• Trickster Mage

  U

  Creature — Human SpellshaperU

  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.
• Paradox Engine

  5

  Legendary ArtifactC

  Paradox Engine untaps all (or many) permanents, refreshing Giant's Boulder's tap activation.
• Filigree Sages

  3U

  Artifact Creature — Vedalken WizardU

  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.
• Elder Druid

  3G

  Creature — Elf Cleric DruidG

  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 Pandorica

  2W

  Legendary ArtifactW

  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.
• Dramatic Reversal

  1U

  InstantU

  Dramatic Reversal untaps all (or many) permanents, refreshing Giant's Boulder's tap activation.
• Blinkmoth Infusion

  12UU

  InstantU

  Blinkmoth Infusion untaps all (or many) permanents, refreshing Giant's Boulder's tap activation.
• Brought Back

  WW

  InstantW

  Brought Back returns creatures from the graveyard to the battlefield, re-firing Giant's Boulder's enter-the-battlefield effect.
• Instrument of the Bards

  G

  Legendary ArtifactG

  Mana loop: net-positive mana cycle between the two cards.
• Reckless Lackey

  R

  Creature — Goblin PirateR

  Mana loop: net-positive mana cycle between the two cards.
• Mr. House, President and CEO

  RWB

  Legendary Artifact Creature — HumanBRW

  Mana loop: net-positive mana cycle between the two cards.
• Currency Converter

  1

  ArtifactC

  Mana loop: net-positive mana cycle between the two cards.
• Jolted Awake

  W

  SorceryW

  Jolted Awake returns creatures from the graveyard to the battlefield, re-firing Giant's Boulder's enter-the-battlefield effect.
• Stark Industries Executive

  R

  Creature — Human AdvisorR

  Mana loop: net-positive mana cycle between the two cards.
• Phelia, Exuberant Shepherd

  1W

  Legendary Creature — DogW

  Phelia, Exuberant Shepherd blinks (exiles and returns) a permanent, re-firing Giant's Boulder's enter-the-battlefield effect.
• Forsworn Paladin

  B

  Creature — Human KnightB

  Mana loop: net-positive mana cycle between the two cards.