I can’t remember exactly which fax attributes there were, but I Think they were Vehicle and Driver attributes that you would give different herofiles. As the playable Driver character you could approach the non playable (not in your team) ‘vehicle’ and then take control of that character for a bit by using the ‘drive’ command. I forget if you had to assign specific drivers to vehicles or not.
I played around with the idea of the ‘gestalt’ attribute for mounted characters, too. Like He-man and Battlecat become a whole new character with He-man mounted on Battlecat. So you’d need 3 meshes and herofiles for that.
As for the Standon part of the question, i’m Not too sure if the stood upon mesh can move. I remember implementing something like that in my wrestling ring map. A steel folding chair was set up, with standon=1 and also ...pickup? Then once a character picked it up the mesh became a folded chair and could be used as a weapon, like a lamppost. If dropped, the mesh stayed in it’s weapon form. This was a few years ago, though, so I’m not sure how well it worked out for furniture. I remember setting it up with the different nifs (set up or folded chair) for the different states, like a lamppost (before it’s ripped out of the ground and after)