Urza's Incubator | Magic: The Gathering
Formats Urza's Incubator is Legal in
Official Oracle Text for Urza's Incubator
Creature spells of the chosen type cost less to cast.
—Rayne, Academy Chancellor
Official Rulings for Urza's Incubator
10/4/2004 : You choose a creature type right as it enters the battlefield, before any continuous effects are applied or trigged abilities trigger.