Piranha,
I am not convinced why it needs the +1 when attacking. It can easily bless to 8 strength with flight/18 moves. That's probably my only complaint now. At 4 turns, 7 strength, ignore city walls it seems OK.
I realize it is not giving its city walls bonus to the stack. However my big concern is that it is an 'ally' and so getting a new hero with 3-4 of these units or popping 2-3 from a ruin will be a very big deal (I'd rather get 3-4 of these units than 3-4 Devils especially in turns 1-20 and maybe even late game too). It means a hero/pegasi and 3-4 of these units (from the new hero/ruin) won't need a siege unit. Once blessed they are just a flying nightmare (would be 11 str if they are 8 str after blessing, +1 attack and with a hero/pegasi) ignoring all terrain as they race around the map. It would be almost impossible to stop / contain them especially in the early part of the game.
In fact the more I think about it the more the flight is what this unit needs to lose (then it can retain the +1 when attacking bonus). That's what makes it most overpowering. As a land based unit it's not nearly as deadly in the early game and will be mostly used for the purpose you are intending (attacking cities full of men) rather than simply racing towards weakly defended cities.
I also realize you aren't adding new units to the game because you have your artist doing the graphics work. But this would have been the ideal place to introduce a new unit: The Sandworm. Basically this unit is the giant Sandworm in the Dune series. It burrows underground (which is why it ignores city walls) and tunnels up to surprise attack (hence the +1 attack). It's native to Desert terrain (would give desert move bonus). That would perfectly give you the unit you are looking for and give you a desert based unit as an added bonus.
KGB