Can't help with most of it I'm afraid but the 0-move thing seems to have a nasty tendency to flag a unit as the last defender - whatever its actual stats.
0Movement doesn't necessarily do that... and if you use 0 Movement in the ancient era with a high D rating- the AI usually will use it as its sole defensive unit.
I remember testing that in one of my scenarios
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I also remember that the AI can use carrier units that walk on 'land' quite well in several games... I know that humans can use them as 'spells' from the grande scenario: "Dungeon"
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