You may cast Mystic Veil as though it had flash. If you cast it any time a sorcery couldn't have been cast, the controller of the permanent it becomes sacrifices it at the beginning of the next cleanup step.
Enchant creature
Enchanted creature has shroud. (It can't be the target of spells or abilities.)
The sacrifice occurs only if you cast it using its own ability. If you cast it using some other effect (for example, if another effect allowed you to cast it as though it had flash), then it won't be sacrificed.