Brass Squire

• WWizards of the Coast2011-06-01
  Official Ruling
  Unlike the equip ability, Brass Squire's ability can be activated whenever you could cast an instant.
• WWizards of the Coast2011-06-01
  Official Ruling
  If one of the targets is illegal when the activated ability resolves, nothing will happen and the Equipment won't move. Notably, if an opponent gains control of either target in response, the Equipment won't move.

Rulings via Scryfall