Artifact, 4 (4)
Rare
{1}, {T}: You may cast a nonland card from your hand without paying its mana cost if it has the same name as a spell that was cast this turn.
It takes two to craft a mirror: a practiced metalsmith to silver one side and her own hazy reflection to polish the other.
Illus. Franz Vohwinkel

10/1/2007: Activating Twinning Glass's ability allows you to cast a single card from your hand as it resolves. It doesn't create a continuous effect, and it doesn't let you cast multiple cards for free.
10/1/2007: It doesn't matter who cast the first spell.
10/1/2007: You can't pay any alternative costs (such as those from evoke or morph) when casting the card. On the other hand, if the card has additional costs (such as those from kicker or buyback), you may pay those.
10/1/2007: If one half of a split card has been cast this turn, you may use Twinning Glass's ability to cast either half of a split card with that name. For example, if Dead from Dead/Gone has been cast, you may use Twinning Glass's ability to cast either Dead or Gone.
Legal in Vintage (Type 1)
Legal in Legacy (Type 1.5)
Legal in Classic (MTGO)
Legal in Commander
Legal in Modern