Mega Beheeyem, based on the Flatwoods Monster
Think this is more fitting to base the mega of an alien encounter like the rest of the line, than just giving it some bigger details. Gave it steel typing as Flatwoods Monster had some metallic clothing, and levitate because well, Beheeyem already does and Flatwoods Monster was said to do as well. And also good to make it immune to ground. Another option could be adaptability as ability.
The shiny one is colored to look more like the Flatwoods Monster, with darker clothing and reddish face.