"Magic Origins", "untap step" (3)
Enchant creature
When Claustrophobia enters, tap enchanted creature.
Enchanted creature doesn't untap during its controller's untap step.
Mage-Ring Responder doesn't untap during your untap step.
: Untap Mage-Ring Responder.
Whenever Mage-Ring Responder attacks, it deals 7 damage to target creature defending player controls.
Tap up to two target creatures.
Spell mastery — If there are two or more instant and/or sorcery cards in your graveyard, those creatures don't untap during their controllers' next untap steps.
Gatherer works better in the Companion app!