J-4 is what looks like a double decker train with white top half & blue bottom half and a yellow stripe separating the two. Doors and drivers window are mid way between the two but there are two levels of passenger windows. Such a thing is an oddity to UK residents used to single deck trains but they do exist - see Wikpedia. Like his brothers he has a hole under the front of the train and a trailing hook behind it.
TF: Remove the loading hook and the connected tube from the back of the train. Flip up the panels on the top of the train and remove the missile launcher from under the back panel. Rotate the entirety of the front and the back relative to the middle of the train so that all of it but especially the grey bits connecting them to the middle are the other way up. Fold the front & back of the train down under the middle to form the legs. Turn the train's nose round so it faces out of the blue side of the leg. Pull the nose out then fold it upwards to form a foot, then fold the wheels back to form a heel spur. Fold the wheels up on the other leg and pull down on them to extend the back of the train. Turn so the wheels are at the back. Fold the back of the train out to form the other foot. (to this point is effectively J-4's combined mode) From here pull the middle of the train up and fold down the remaining piece of blue side on the front. Fold the arms down & out of the train roof panels. Rotate the panel in the roof of the middle so the head is revealed then raise it up by folding back the ball joint on the base of the neck and folding forward the head. Slot the missile launcher and barrel together to form the hand weapon, flip the peg out and place in J-4's hand. .
J-4 has excessively large legs compared to the rest of the body - can you tell it's meant to be the legs for JRX ? - and the small proportions of the upper body are emphasised by the *HUGE* shoulder pads that he has. He bends & turns at the knees and his hips move forward & back and to the sides. The neck has a ball joint at the base and a joint that lets the head lean back at the top. He's got ball jointed shoulders and double hinged elbows on his long but thin arms.
Decent train. Disproportionately sized robot betraying it's combined toy function.
J-4 is Car Robots Toy C-014 and also features in the JRX Giftset C-015
Midnight Express was sold as a Mega sized toy making it poor value for money as it's essentially a large deluxe toy. Of course by this point the UK had turned it's back on the Mega size class though some of the Bullet Train assortment were later available in the UK as "grey imports" through toy shops.
All three of the Bullet Train team and their combined forms had their names reused for the Universe release of Six Train.