Demons need to be reduced in power. Also, I would like to see...
Devils - I would like this to be the equal opposite of Red Dragons, so instead of having 8 negate aura and 2 fear, it should have 10 fear, and no negate aura. I think the Great Archon has the negate aura covered, so what is the point. Further, the attack points should be moved up to 40. Make the cost the same as well. That would make this the equivalent of a red dragon, but the dark side.
Green Dragon - This is a tough unit to want right now. Why take a green dragon when a worm or elemental has the same heart bonus with less production time, great flying? Also, worms, elementals, and gryphons have attack bonus in a city which places their attack points above a green dragon, so why not take those cheaper units. Either, the time needs to be three turns with the attack value lowered to 30, with a lowered cost for production; or an extra attack value needs to be added. It could have attack value in a city, ability to negate walls, be a stronger elepphant, it could have +5 leadership, +10 when attacking... something.
Gryphons - This is kind of an overpowered unit. They are basically flying spiders with better movement. I think they are too strong though. The attack bonus on a city should total no more than 40, so they are not stronger than a spider. The spider is limited because it moves so slow, and can easily be caught in a field or in the mountains. The gryphon isn't fast, but it can get to a city before it is seen more often. I think this is too much of an advantage, so 40. Fire Elementals could probably be reduced as well.