'Extortion', The Storm Sword.

Can only equip to Em, Daughter of Storms.
Equip 2.
When equipped creature deals combat damage to
a creature, choose one:
Steal: Gain control of target equipment that is
equipped to that creature.
Strand: Tap that creature, it doesn't untap during
its controllers next untap step.
Storm: The next instant or sorcery spell you cast
this turn that targets that creature gains 'Storm.'