The Illogic of Flight

[Archonsod]

Flying archers would certainly be illogical (how would they aim the bow and stay airborne at the same time?). As for flying mages, perhaps the effort to stay airborne affects their concentration for spells, or perhaps they're simply unwilling to risk tiring themselves out with spells while being a few hundred feet off the ground.
Alternatively, perhaps flying units are simply unwilling to place themselves in a position which puts them in line of sight (and possibly attack range) of every archer, mage and priest in the opposing army?

Not sure about immunity to trample. Presumably the trampling unit would simply wait until they land. On the other hand, a flying unit would have an easier time avoiding the unit, but then any sufficiently agile unit should be able to 'dodge' a trample in some manner (elephants for example, are not known for being nimble).

The problem with coastal movement is handling combat (should any occur) between underwater and airborne forces. Unless of course it's treat in a similar manner to sailing (i.e. the unit effectively skips the water province).

[Xietor]

well,

a skilled natural flyer would never "land" during combat, so the trampler would be picked to pieces while he waited.

Creatures that are skilled in flying, and attack with claws or beak, are going to attack the head, neck, eyes. they are not going to land and claw at the elephant's feet.

I think a demon with wings may likely "land" on the elephant's spinal cord where the elephant could not reach it and attack it from there, if it landed at all.

In short, i see a big difference in units that can fly, but have to aim bows or cast spells, and units that are "natural" air units that attack with their nature-given weapons, teeth claws etc.

The latter i do not see getting trampled. Agile units on the ground do get a bonus to avoid being trampled. But obviously if there are 10 elephants, which one are you going to dodge?