This may have already been asked but im not sure. If I play say Darkrai EX from DEX would i need to also have a darkrai from legendary tressures in my deck. Or if i dont need it in my deck do i need to have a copy of the reprint with me.
No. You can play any copy of any card that has been reprinted. You can even play reprinted trainers as long as they have the same name (except for Computer Search because it is an Ace Spec).