Figured I might note that if you want to get really nitty gritty, then the damage heat would do to a person is technically based in movement on a microscopic scale, so Siberian being unharmed by Sundancer’s power does still jive with the “immovable object” model on some level. Of course when you get that granular the difference between “immovable object” and “physical form that is fundamentally impossible to compromise” is essentially nonexistent.
I suppose that’s true, and it is something I have given some thought. I’ve been thinking along the lines that heat transfer by radiation (like sunlight) wouldn’t be moving the atoms directly like heat transfer by contact would. That might not really hold up, though, especially since temperature is movement.