Enchantment, 3BB (5) As Conspiracy comes into play, choose a creature type. Creature cards you own that aren't in play, creature spells you control, and creatures you control are the chosen type.1
Illus. Jeff Easley
This replaces all creature types on those cards for as long as it is in play. [MM FAQ 1999/09/22]
Choosing Legend as the creature type does not make creature legendary. [D'Angelo 2005/10/01]
Choosing Wall as the creature type does not give the creatures Defender or make them unable to attack. [D'Angelo 2005/10/01]
This can grant a creature type to animated lands and artifacts that would otherwise have no creature type. [D'Angelo 2000/10/08]
It does not replace any use of creature types in card text. For example, it will not change Mercenary Informer to be able to pull a different creature type. [D'Angelo 2000/09/07]
Note - Also see Rule 212.1e for details on choosing creature types.