Armorer

The armorer is a HORRIFICLY slow unarmed bulky unit, however it makes up for that with its HUGE shell, until you break through its shell its practically unkillable, as you fire damage starts to show up on each of the "plates" and eventually it will shatter, there are 3 layers, once you have broke 3 layers (on the same spot) you can get to its weak underlayer and kill it, it has weakpoints but they have slightly stronger layers over them and have 4 layers.

Mega version
The mega version is a much rarer and even tougher varient, even slower, EVEN STRONGER shell, an extra layer to said shell (4 for normal areas, 5 for weak spots), and a gun mounted on top.

Light version
Only has 2 layers (3 for weak spots), fairly weaker (still considerably tough) but more common and 2x faster than the origonal.