These Heavy Weapon units are starting to get INVOLVED. On the surface, this one is a booster that can be mounted on the back of a Frame Arms or Frame Arms Girl unit of your choosing. Look a little deeper though, and it can also be used as high-mobility type legs OR combined with the separately-sold Raptor Unit into its own standalone support unit! Of course the entire set uses 3mm pegs and holes so that it's compatible with all other Frame Arms and MSG accessories!