Ok here's my scenario, I've got shorecrasher elemental on the battlefield and then I play evil twin as a copy of the elemental, then I pay the 1B to bounce evil twin which is really the copy from exile later, what happens? Because it says he enters as whatever but does it enter facedown I'm stuck on this one.
Evil Twin stops being a copy of Shorecaster Elemental as soon as it leaves the battlefield, but the ability can still "see" it in exile and return it to the battlefield face down.
Entering face down means Evil Twin enters as a colorless 2/2 with no abilities, so it can't copy anything, and will probably be stuck face down on the field.
Your Evil Twin will reenter the battlefield face-down as a 2/2 creature with no characteristics. Because Evil Twin does not have morph or megamorph, it will be unable to turn itself face-up. If something else turns it face-up (with Break Open or a similar effect, for example), it would turn face-up as a 0/0 Evil Twin and die as a state-based action.
Entering face down means Evil Twin enters as a colorless 2/2 with no abilities, so it can't copy anything, and will probably be stuck face down on the field.