An outlandish brute. May not understand English...or any language, for that matter. A man out of time: big, bearded, and even with no knowledge of what a gun is, is a natural at shooting.
Due to a freak accident with two individuals and a time-travelling car, the Caveman stowed away and is now trapped in the future, all alone. He does think he can put this to good use: he can save his friends from extinction. See, before he was whisked away to the future, he was with his family, about to watch his planet be destroyed by a meteor. If you count a pack of dinosaurs as "family". Looking back, he realized this was his chance to save his friends and family from utter destruction. He was going to find a way back, fight the meteor (yes, the actual meteor), and save everyone.
Basically The Caveman will throw Rib Bones, and they'll start to curve around the longer they travel, like a boomerang. The weapon itself fires and reloads slower, but each individual bone does more damage.
It's a half item/half weapon in the sense of you having to charge up the club and then hit a wall with it, causing it to reveal, or not reveal, a secret room. It does not actually damage enemies when used.
(The name Carlo is a reference to the dinosaur Arlo from The Good Dinosaur.) It acts as an orbital, having a chance to reflect enemies' bullets when they make contact with it. Sort of like a mashup of the Rolling Eye and the Orange Guon Stone.