Confidence:StrongSolidPlausibleTentativeSpeculative

• Magus of the Candelabra

  G

  Creature — Human WizardG

  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.
• Innocuous Researcher

  3G

  Creature — Centaur DetectiveG

  Innocuous Researcher untaps all (or many) permanents, refreshing Castle Doom's tap activation.
• Fiery Gambit

  2R

  SorceryR

  Fiery Gambit untaps all (or many) permanents, refreshing Castle Doom's tap activation.
• Candelabra of Tawnos

  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.
• Soundwave, Sonic Spy // Soundwave, Superior Captain

  1WUB

  Legendary Artifact Creature — Robot // Legendary ArtifactBUW

  Both cards produce the same kind of effect (shared token subtype).
• Ultron the Annihilator

  3BB

  Legendary Artifact Creature — Robot VillainB

  Both cards produce the same kind of effect (shared token subtype).
• Saryth, the Viper's Fang

  2GG

  Legendary Creature — Human WarlockG

  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.
• Prophet of Kruphix

  3GU

  Creature — Human WizardGU

  Prophet of Kruphix untaps all (or many) permanents, refreshing Castle Doom's tap activation.
• Bumi, Unleashed

  3RG

  Legendary Creature — Human Noble AllyGR

  Bumi, Unleashed untaps all (or many) permanents, refreshing Castle Doom's tap activation.
• Ultron, Unlimited

  1UB

  Legendary Artifact Creature — Robot VillainBU

  Both cards produce the same kind of effect (shared token subtype).
• Big Mother Mouser

  4

  Artifact Creature — RobotC

  Both cards produce the same kind of effect (shared token subtype).
• Ravenous Robots

  1R

  Artifact Creature — RobotR

  Both cards produce the same kind of effect (shared token subtype).
• Retrieve the Esper

  3U

  SorceryU

  Both cards produce the same kind of effect (shared token subtype).
• Securitron Squadron

  1W

  Artifact Creature — RobotW

  Both cards produce the same kind of effect (shared token subtype).
• 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.
• Seedborn Muse

  3GG

  Creature — SpiritG

  Seedborn Muse untaps all (or many) permanents, refreshing Castle Doom's tap activation.
• Mechan Assembler

  4U

  Artifact Creature — Robot ArtificerU

  Both cards produce the same kind of effect (shared token subtype).
• Wilderness Reclamation

  3G

  EnchantmentG

  Wilderness Reclamation untaps all (or many) permanents, refreshing Castle Doom's tap activation.
• Roadkill Rodney

  2

  Artifact Creature — RobotC

  Both cards produce the same kind of effect (shared token subtype).
• Mysterio, Master of Illusion

  3U

  Legendary Creature — Human VillainU

  Both cards produce the same kind of effect (shared token subtype).
• Sword of Feast and Famine

  3

  Artifact — EquipmentC

  Sword of Feast and Famine untaps all (or many) permanents, refreshing Castle Doom's tap activation.
• Madame Hydra

  2BR

  Legendary Creature — Human VillainBR

  Both cards produce the same kind of effect (shared token subtype).
• Crimson Cowl, Master of Evil

  2B

  Legendary Creature — Human VillainB

  Both cards produce the same kind of effect (shared token subtype).
• Kavaron Harrier

  R

  Artifact Creature — Robot SoldierR

  Both cards produce the same kind of effect (shared token subtype).
• Beledros Witherbloom

  5BG

  Legendary Creature — Elder DragonBG

  Beledros Witherbloom untaps all (or many) permanents, refreshing Castle Doom's tap activation.