Confidence:StrongSolidPlausibleTentativeSpeculative

• Iron Spider, Stark Upgrade

  3

  Legendary Artifact Creature — Spider HeroC

  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.
• Teysa Karlov

  2WB

  Legendary Creature — Human AdvisorBW

  Teysa Karlov makes Costume Closet's triggered ability trigger an additional time — each time it fires, you get it twice. Value, not a loop.
• Drivnod, Carnage Dominus

  3BB

  Legendary Creature — Phyrexian HorrorB

  Drivnod, Carnage Dominus makes Costume Closet's triggered ability trigger an additional time — each time it fires, you get it twice. Value, not a loop.
• Intellectual Offering

  4U

  InstantU

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

  2U

  EnchantmentU

  Unstoppable Plan untaps all (or many) permanents, refreshing Costume Closet's tap activation.
• Ozolith, the Shattered Spire

  1G

  Legendary ArtifactG

  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.
• Mirror Room // Fractured Realm

  2U5UU

  Enchantment — Room // Enchantment — RoomU

  Mirror Room makes Costume Closet's triggered ability trigger an additional time — each time it fires, you get it twice. Value, not a loop.
• Unwinding Clock

  4

  ArtifactC

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

  3GG

  Creature — SpiritG

  Seedborn Muse untaps all (or many) permanents, refreshing Costume Closet's tap activation.
• Paradox Engine

  5

  Legendary ArtifactC

  Paradox Engine untaps all (or many) permanents, refreshing Costume Closet's tap activation.
• Dramatic Reversal

  1U

  InstantU

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

  12UU

  InstantU

  Blinkmoth Infusion untaps all (or many) permanents, refreshing Costume Closet's tap activation.
• Kurkesh, Onakke Ancient

  2RR

  Legendary Creature — Ogre SpiritR

  Costume Closet has activated abilities that aren't mana abilities, fueling Kurkesh, Onakke Ancient's activation-trigger.
• Rings of Brighthearth

  3

  ArtifactC

  Costume Closet has activated abilities that aren't mana abilities, fueling Rings of Brighthearth's activation-trigger.