Yes, dragons we're suggested a long time ago.
I like some of these ideas, so will make my comments ...
I think they should be 1 per player & only available from their Main.
Powering them up should be with troops only, if they were real, the number of troops lost to them while taming / training it would happen anyway.
The more powerful the troop sacrificed, the more power the dragon gains.
They should damage random buildings ... not target specific buildings.
Enemy troops killed should be a small percentage (1%) ... in real life, most would take cover when they see it.
They should also take damage from defending archers only (damage = 25% of normal due to flying & being a fast moving target) & have the possibilty to be killed outright.
The chances to lose them should be a low possibility (5%), but they don't just roam free indefinitely ... lost dragons should last for 12 hours after being lost & do damage to random castles anywhere on the map while they feed.
A player that loses or has a dragon killed, can restart a new dragon after 24 hours of it being lost, but it starts at the lowest level again.