The Super Robot Wars/Taisen games are games that, by United States laws, would never get made because of the massive amount of rights information. Fortunately, Japanese creators never let the legal system get in the way of a cool concept: Teaming up any and every super robot and mecha from Japan ever devised (from anime).
Super Robot Wars J featured one of the most massive final bosses of all time (not really) and Boss Borot. It's inevitable they would meet:
I love that boss's attack.