Xenic Poltergeist

Oracle Text

T: Until your next upkeep, target noncreature artifact becomes an artifact creature with power and toughness each equal to its converted mana cost.

Card Rulings

10/4/2004 Wears off at the beginning of the upkeep, not during upkeep.
8/1/2008 A noncreature permanent that turns into a creature can attack, and its abilities can be activated, only if its controller has continuously controlled that permanent since the beginning of their most recent turn. It doesn’t matter how long the permanent has been a creature.