Colfenor's Urn | Magic: The Gathering
Formats Colfenor's Urn is Legal in
Official Oracle Text for Colfenor's Urn
At the beginning of the end step, if three or more cards have been exiled with Colfenor's Urn, sacrifice it. If you do, return those cards to the battlefield under their owner's control.
Official Rulings for Colfenor's Urn
10/1/2007 : The second ability forces you to sacrifice Colfenor's Urn. If the ability triggers and the Urn isn't sacrificed (because it left the battlefield or changed controllers, for example), the exiled cards won't be returned to the battlefield.
10/1/2007 : The first ability triggers when a token creature with toughness 4 or greater is put into your graveyard. However, that token will cease to exist before Colfenor's Plans can exile it.