Nifflas' basic movement widget works nicely for movement on backdrop objects, but in order to create more interesting platforming, I'd like to make it work with active objects. It appears to be as simple as adding an OR to the "Y Move" group such that the events that keep the character standing on a backdrop also apply to active objects, BUT I guess it's not so simple.
The best I can do is add a condition for active objects in which I manually set "_Y Offset", "_Y Speed", and "_Standing On Ground" to 0,0, and 1 respectively. But this results in imperfect collision detection where my character sinks into the active. It looks like the amount the character sinks is correlated to the height from which I jump onto the active (is that the _Y Speed ?).