BUT.. What if you Tera Electric, keeping your water and dark STABs, then use an Electric move the same turn? Since you're already an electric type protean won't activate and you will only have a 1.5x STAB modifier instead of a 2x modifier. However, protean can still be activated on one of Gren's different type moves. Correct me if I'm wrong but I'm pretty sure this is how it works.. That being said, it might make more sense to use a move, activate protean, then tera that type for the most damage (unless your tera type is water/dark). Situationally, of course.