how do we know what gender mimikyu is if looking under its costume can make you die of shock?

Mimikyu will often attempt to mimic pikachu of their chosen gender. So if you look very closely, a female mimikyu will often be holding a stick with a notch in it, if she doesn’t apply makeup to her costume. (Some mimikyu use cartoon pikachu as their models.) Male mimikyu will conversely look for the stick with the cleanest end possible.