We know of or have assumed the existence several flying units in AoM. They are; Pegasus, Phoenix, Raven, Nidhogg, Bellerophon, Griffin and Roc. There may be others as well.

I'll divide them into three speculative categories; scouts, transports and attackers.

Scouts - Pegasus, Phoenix and Raven. They are speculated to have no value as attackers and are only scout units.
Transports- Griffin and Roc. Have been rumoured as having the ability to carry units over walls and across the map. Seems like they'll have little value as attackers themselves. Kinda like transport ships in the air.
Attackers - Nidhogg and Bellerophon. Nidhogg breathes fire and Bellerophon is pictured with a sword or a spear. This leads me to conclude that the Nidhogg is a ranged attacker and Bellerophon is a meele attacker.

Keep in mind that the Nidhogg is summoned by a god power. Certainly, the Nidhogg is powerful, but since its summoned by a GP it's definately limited.

This leads me to the conclusion that there will be no trainable units that are flying and ranged. Do you agree with this assumption? I'm happy about this (if it's true) because flying ranged units are like cav archers that you can never catch. This theory fits in with comments by ES that flying units are not a major part of game balance.

Another thing about flying units I don't understand is the griffin and the roc. Are they second MU's granted by minor gods like Scylla is? I don't believe that they (or any MU) would be relic only as some have suggested. So where does the griffin fit into the Greek tech tree?

Also, if I forgot any flying units feel free to bring them up. I'll put them in a category.