Monsterous was produced in 1987. Bandai & Tonka were still aiming for the robot monster stuff, and that is what produced this oddity. Again we have six pieces to combine Monsterous as we did with the Puzzler. The posability is lessened but the piece is tighter and combines much easier. The detailing and imagination put into these guys are amazing, but playbaility was sacrificed. Some of the vehicles are confusing at best, and it seems they focused on making a nice looking robot than individual robots. From this we also lost poseability in the figures.
Monsterous combiners can be found individually carded or found in a gift set. They were released in Europe, and in Japan. Japan though had them in various colors and they were called Satan 6.