There are two positions which could be called Superman.
- the Boardman one which has the arms pointing way forward like Superman in flight but the legs still pedal. This is an aggressive aero timetrial position using a long stem and ski-pole length aerobars to reduce the angle of the upper arm respective to the incoming air - essentially reducing the effective frontal area.
Note his head is looking forward but his spine is flattish and angled down at the top. This is a horribly uncomfortable position in which to ride. Here thats okay because he's on a track with no road traffic (its likely he's alone on the track.)
The saddle in use is hard to see but its nothing special - he's still pedalling so a normal time-trial saddle will be used. Weight is still important, but there are no climbs on a track. Instead its all about getting the rider into their most aerodynamic position possible, and then allowing whatever comfort is possible without affecting their aero position.
- there's the viral-video position which is essentially planking on the bike, coasting with one's legs out the back like an airplane tail.
As you can see - that's Michael Guerra (left, in yellow) riding a vigorelli fixed gear road bike. There's nothing special about his saddle, which can be glimpsed in the full video
In no way is this a good idea on a road, or anywhere uncontrolled. Boardman's bike is a track bike, with no gears and no brakes. This is workable because the track is isolated.
Doing this kind of thing on the road is foolish, and risks yourself, and worse, risks others. Notice that any emergency reaction will have him off the bike because there is no third point of contact with the feet, and the saddle contact is only gravity. At the end of the video, they have to divert around a mobility scooter and frankly have insufficient margin for error.
If you intend to ride like this on the road, just don't.