I had some small advances, but I can't seem to stop his combination of ghost riders and Tartarians. He hit me with about 7 Ghost Riders last turn. Where does he get the gems if he's also pelting you with GR?
He is also taking my provinces now so it doesn't look good.
I killed one of his Air Queens last turn (along with a few air elementals and some sylphs - mabye that group that you faced?). I also killed an Ice Devil and luckily (no pun intended) charmed one of his Tartarians, so now that particular bad boy is working for the good guys in green
I took one of his castles as well in that battle, but it's a farm province and didn't have any gem sites.
In the Feldan Forest, he has another Air Queen and a Tartarian along with about 70 odd pieces of other crap. He has about 20 Jade Sorceress hanging around, too.
I continue to try to pressure him, but it's not looking good. But, I'm going to go down swinging, and you never know what can happen, so keep at