ethereal on turns 1-3

"can be moved through but not attacked through"

These are both interesting ideas. Not sure I would go as far as changing ghosts into either of them, but they could definitely be used for something. for example, the illusionist is (eventually) supposed leave an illusion behind every time he teleports, which are kinda harmless for obvious reasons, but if they blocked ally movement it would be silly and if they don't block enemy units then it's kinda pointless, so there is some idea of conditional transparency where illusions block only the enemy and that is one of their primary purposes - I think other conditional transparency effects could be used for similar things.