Shuko

• WOTC Official Reminder Textofficial rules
  Equip — Equip [cost] ([cost]: Attach to target creature you control. Equip only as a sorcery.)

• WWizards of the Coast2013-04-15
  Official Ruling
  You may activate this card’s equip ability targeting the creature that it is currently attached to, even if it’s the only creature you control. Since the equip ability costs zero, you can do this as many times as you like during your main phases, though it generally won’t do anything.

Rulings via Scryfall