Magus of the Unseen

Oracle Text

1U, T: Untap target artifact an opponent controls and gain control of it until end of turn. It gains haste until end of turn. When you lose control of the artifact, tap it.

Card Rulings

10/4/2004 You may target an untapped artifact with this ability.
10/4/2004 The artifact taps after returning to the opponent (if it is not already tapped), so any abilities triggered off it tapping happen at that time.
10/1/2008 You tap the artifact when you lose control of it for any reason — because Magus of the Unseen’s effect ends, or because a spell or ability causes another player to gain control of it.
10/1/2008 The artifact will gain haste whether or not it’s a creature. Of course, if it’s not a creature, haste will have no particular effect.