>>12302605Though I know that it is completely grabbing at straws and is more than likely 100% false, I have a theory on how this could happen until proven otherwise.
As many have pointed out, the triangle on the new poke resembles a solar panel. Along with its secondary typing as normal, it makes me think that there could be a split evolution. If the pokemon goes through the correct requirements to evolve whatever that may be, but during night, the pokemon evolves into mawile because it doesn't have the energy needed to create the electric typing that it would evolve into if it was during the day