Stay Hidden, Stay Silent

Because face-down creatures don't have a name, they can't have the same name as any other creature, even another face-down creature.

A permanent that turns face up or face down changes characteristics but is otherwise the same permanent. Spells and abilities that were targeting that permanent and Auras and Equipment that were attached to that permanent aren't affected unless the new characteristics of the object change the legality of those targets or attachments.

Any time you have priority, you can turn a manifested permanent you control face up by revealing that it's a creature card (ignoring any copy effects or type-changing effects that might be applying to it) and paying its mana cost. This is a special action. It doesn't use the stack and can't be responded to.