Dude! DUDE! F'cking awesome stuff here. First, the spear is well done, the lighting is superb, I like that it looks like the metal is actually heated to cherry as opposed to just emitting orange light. Two, that suit or armor is FUCKING SWEET. Love the bulky limbs and segmented pieces, and it looks like it was either handbuilt or put together piecemeal. Is this character from the same universe as your tank critter?
It's the sharp light on the very edge of the subject caused by a strong light behind or to the left/right rear of the subject. This give a strong bright outline and is used a lot in entertainment to help highlight things from the background.