1 If memory serves, Magic Spirits have Pathfinding. Since I can't find a reference online for some reason: Pathfinding units use half a movement point to move over any terrain, and they also share this benefit with every unit in the stack. Magic Spirits only have one movement point as well, but they can move two spaces a turn. However, Pathfinding is buggy, so although it seems weird that it lets Shadow Demons move an extra space, that is one of the few places where it's actually working properly (perhaps because the Shadow Demons fly?).

2

They don't have pathfinding. They're incorporeal, which gives them the ability to cross terrain at half-a-move per square. Wraiths do the same, and anything with the Wraithform spell does, too.

That's why Great Wyrms with Wraithform move 6 on the strategic map.

But where pathfinding even on one unit affects the whole stack, Wraithform doesn't. If any unit in the stack is not incorporeal, the entire stack moves at the slower speed.

Shadow Demons are not incorporeal; that's why when a stack is made up exclusively of Shadow Demons it moves speed 1. If you added a pathfinding unit to that, it would double the speed. I haven't tested it, but if you put the pathfinding spell on any one of them, it should, too.

And presumably if you did Wraithform on all of them, it would, too. But adding a Magic Spirit to the stack shouldn't.

I've got a save game where I can test that. I'll do it in the morning.

3

Here's what I found:

Shadow Demons are noncorporeal. They have a movement of 1, and that should mean they cover two spaces per turn, but they actually move one.

If you put pathfinding on a Shadow Demon, it has no effect. Still moves one.

If you have Shadow Demons and a Ranger in the same stack, it moves two.

Magic Spirits are noncorporeal. With a listed movement of one, they move two because of the noncorporeal bonus.

Magic Spirits are not pathfinders. A stack consisting of a Magic Spirit and a Settler moves one, not two. A stack of a Settler and a Ranger moves two.

You can't put Wraithform on a Shadow Demon. It tells you that it already has it.

Conclusion: I think that in the name of game balance, an exception was made for Shadow Demons to slow them down, but there's a bug in the code which kicks in when Shadow Demons are stacked with Magic Spirits.

4 Interesting! I was so sure Magic Spirits were pathfinders, but it has been quite a while since I played a game of MoM. Maybe I'll get around to one tomorrow.