Most games simply make two physics spaces for on-the-train and off-the-train. Then you have to round off the edges of the transition. Theres many funny videos where that goes wrong in AAA engines, like a guy hanging on the car making the car have a bulge in it’s “real world” physics space etc.
For a simple platform you should simply by able to put a physics object on it and it will move along but that won’t work when you modify the velocity directly (as its the only result of the physics). So not for BetterCharacter.