My theory is that legacy mechs were MASSIVE since in reloaded it shows these kinds of things, it becomes noticeable when you look at the drone, the DRONE is already bigger than the mechs we have currently. Now imagine GODMODE....
The Saurus Rifle is even bigger than the trees, the starter weapon you could see on the login menu as well..
Fortune boxes, they have a chance to drop a legendary.
Fastest way to get them is the dry lands boss. The general prefered level is Overlord's Den mission 8 on insane, but depending on your mech, it might not be possible yet.